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                                                                   EXHIBIT 10.56


                          SUPPLEMENTAL INDENTURE TO BE
                     DELIVERED BY GUARANTEEING SUBSIDIARIES

         SUPPLEMENTAL INDENTURE (this "Supplemental Indenture"), dated as of
March 10, 2003, among AMI Instruments, Inc., an Oklahoma corporation, Apcom,
Inc., a Maryland corporation, Broadcast Sports Inc., a Delaware corporation,
Celerity Systems Incorporated, a California corporation, EER Systems, Inc., a
Virginia corporation, Electrodynamics, Inc., an Arizona corporation, Henschel
Inc., a Delaware corporation, Hygienetics Environmental Services, Inc., a
Delaware corporation, Interstate Electronics Corporation, a California
corporation, KDI Precision Products, Inc., a Delaware corporation, L-3
Communications AIS GP Corporation, a California corporation, L-3 Communications
Analytics Corporation, a California corporation, L-3 Communications Atlantic
Science and Technology Corporation, a New Jersey corporation, L-3 Communications
Aydin Corporation, a Delaware corporation, L-3 Communications ESSCO, Inc., a
Delaware corporation, L-3 Communications ILEX Systems, Inc., a Delaware
corporation, L-3 Communications IMC Corporation, a Connecticut corporation, L-3
Communications Integrated Systems L.P., a Delaware limited partnership, L-3
Communications Investments, Inc., a Delaware corporation, L-3 Communications
Security and Detection Systems Corporation Delaware, a Delaware corporation, L-3
Communications Security and Detection Systems Corporation California, a
California corporation, L-3 Communications SPD Technologies, Inc., a Delaware
corporation, L-3 Communications Storm Control Systems, Inc., a California
corporation, L-3 Communications TMA Corporation, a Virginia corporation, L-3
Communications Westwood Corporation, a Nevada corporation, MCTI Acquisition
Corporation, a Maryland Corporation, Microdyne Communications Technologies
Incorporated, a Maryland corporation, Microdyne Corporation, a Maryland
corporation, Microdyne Outsourcing Incorporated, a Maryland corporation, MPRI,
Inc., a Delaware corporation, Pac Ord Inc., a Delaware corporation, Power
Paragon, Inc., a Delaware corporation, Ship Analytics, Inc., a Connecticut
corporation, Ship Analytics International, Inc., a Delaware corporation, Ship
Analytics USA, Inc., a Connecticut corporation, Southern California Microwave,
Inc., a California corporation, SPD Electrical Systems, Inc., a Delaware
corporation, SPD Holdings, Inc., a Delaware corporation, SPD Switchgear Inc., a
Delaware corporation, SYColeman Corporation, a Florida corporation, Telos
Corporation, a California corporation, Troll Technology Corporation, a
California corporation, Wescam Air Ops Inc., a Delaware corporation, Wescam Air
Ops LLC, a Delaware limited liability company, Wescam Holdings (US) Inc., a
Delaware corporation, Wescam Incorporated, a Florida corporation, Wescam LLC, a
Delaware limited liability company, Wescam Sonoma Inc., a California corporation
and Wolf Coach, Inc., a Massachusetts corporation (each, a "Guaranteeing
Subsidiary", and collectively, the "Guaranteeing Subsidiaries"), each a
subsidiary of L-3 Communications Corporation (or its permitted successor), a
Delaware corporation (the "Company"), the Company and The Bank of New York, as
trustee under the indenture referred to below (the "Trustee").

                              W I T N E S S E T H:
                              - - - - - - - - - -

                  WHEREAS, the Company has heretofore executed and delivered to
the Trustee an indenture (the "Indenture"), dated as of December 11, 1998
providing for the issuance of an

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                                                                               2


aggregate principal amount of up to $300,000,000 of 8% Senior Subordinated Notes
due 2008 (the "Notes");

                  WHEREAS, the Indenture provides that under certain
circumstances the Guaranteeing Subsidiaries shall execute and deliver to the
Trustee a supplemental indenture pursuant to which the Guaranteeing Subsidiaries
shall unconditionally guarantee all of the Company's Obligations under the Notes
and the Indenture on the terms and conditions set forth herein (the "Subsidiary
Guarantee"); and

                  WHEREAS, pursuant to Section 4.13 of the Indenture, the
Trustee is authorized to execute and deliver this Supplemental Indenture.

                  NOW THEREFORE, in consideration of the foregoing and for other
good and valuable consideration, the receipt of which is hereby acknowledged,
the Guaranteeing Subsidiaries and the Trustee mutually covenant and agree for
the equal and ratable benefit of the Holders of the Notes as follows:


                  1.    CAPITALIZED TERMS. Capitalized terms used herein without
definition shall have the meanings assigned to them in the Indenture.

                  2.    AGREEMENT TO GUARANTEE. Each Guaranteeing Subsidiary
hereby agrees as follows:

                        (a)  Each Guaranteeing Subsidiary, jointly and severally
                             with all other current and future guarantors of the
                             Notes (collectively, the "Guarantors" and each, a
                             "Guarantor"), unconditionally guarantees to each
                             Holder of a Note authenticated and delivered by the
                             Trustee and to the Trustee and its successors and
                             assigns, regardless of the validity and
                             enforceability of the Indenture, the Notes or the
                             Obligations of the Company under the Indenture or
                             the Notes, that:

                             (i)  the principal of, premium and interest on the
                                  Notes will be promptly paid in full when due,
                                  whether at maturity, by acceleration,
                                  redemption or otherwise, and interest on the
                                  overdue principal of, premium and interest on
                                  the Notes, to the extent lawful, and all other
                                  Obligations of the Company to the Holders or
                                  the Trustee thereunder or under the Indenture
                                  will be promptly paid in full, all in
                                  accordance with the terms thereof; and


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                                                                               3

                             (ii) in case of any extension of time for payment
                                  or renewal of any Notes or any of such other
                                  Obligations, that the same will be promptly
                                  paid in full when due in accordance with the
                                  terms of the extension or renewal, whether at
                                  stated maturity, by acceleration or otherwise.

                        (b)  Notwithstanding the foregoing, in the event that
                             this Subsidiary Guarantee would constitute or
                             result in a violation of any applicable fraudulent
                             conveyance or similar law of any relevant
                             jurisdiction, the liability of each Guaranteeing
                             Subsidiary under this Supplemental Indenture and
                             its Subsidiary Guarantee shall be reduced to the
                             maximum amount permissible under such fraudulent
                             conveyance or similar law.

                  3.    EXECUTION AND DELIVERY OF SUBSIDIARY GUARANTEES.

                        (a)  To evidence its Subsidiary Guarantee set forth in
                             this Supplemental Indenture, each Guaranteeing
                             Subsidiary hereby agrees that a notation of such
                             Subsidiary Guarantee substantially in the form of
                             Exhibit F to the Indenture shall be endorsed by an
                             officer of such Guaranteeing Subsidiary on each
                             Note authenticated and delivered by the Trustee
                             after the date hereof.

                        (b)  Notwithstanding the foregoing, each Guaranteeing
                             Subsidiary hereby agrees that its Subsidiary
                             Guarantee set forth herein shall remain in full
                             force and effect notwithstanding any failure to
                             endorse on each Note a notation of such Subsidiary
                             Guarantee.

                        (c)  If an Officer whose signature is on this
                             Supplemental Indenture or on the Subsidiary
                             Guarantee no longer holds that office at the time
                             the Trustee authenticates the Note on which a
                             Subsidiary Guarantee is endorsed, the Subsidiary
                             Guarantee shall be valid nevertheless.

                        (d)  The delivery of any Note by the Trustee, after the
                             authentication thereof under the Indenture, shall
                             constitute due delivery of the Subsidiary Guarantee
                             set forth in this Supplemental Indenture on behalf
                             of each Guaranteeing Subsidiary.

                        (e)  Each Guaranteeing Subsidiary hereby agrees that its
                             obligations hereunder shall be unconditional,
                             regardless of the validity, regularity or
                             enforceability of the Notes or the Indenture, the
                             absence of any action to enforce the same, any
                             waiver or consent by any Holder of the Notes with
                             respect to any provisions of the Notes or the
                             Indenture, the recovery of any judgment against the
                             Company, any action to enforce the same or any
                             other


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                                                                               4


                             circumstance which might otherwise constitute a
                             legal or equitable discharge or defense of a
                             guarantor.

                        (f)  Each Guaranteeing Subsidiary hereby waives
                             diligence, presentment, demand of payment, filing
                             of claims with a court in the event of insolvency
                             or bankruptcy of the Company, any right to require
                             a proceeding first against the Company, protest,
                             notice and all demands whatsoever and covenants
                             that its Subsidiary Guarantee made pursuant to this
                             Supplemental Indenture will not be discharged
                             except by complete performance of the obligations
                             contained in the Notes and the Indenture.

                        (g)  If any Holder or the Trustee is required by any
                             court or otherwise to return to the Company or any
                             Guaranteeing Subsidiary, or any Custodian, Trustee,
                             liquidator or other similar official acting in
                             relation to either the Company or such Guaranteeing
                             Subsidiary, any amount paid by either to the
                             Trustee or such Holder, the Subsidiary Guarantee
                             made pursuant to this Supplemental Indenture, to
                             the extent theretofore discharged, shall be
                             reinstated in full force and effect.

                        (h)  Each Guaranteeing Subsidiary agrees that it shall
                             not be entitled to any right of subrogation in
                             relation to the Holders in respect of any
                             obligations guaranteed hereby until payment in full
                             of all obligations guaranteed hereby. Each
                             Guaranteeing Subsidiary further agrees that, as
                             between such Guaranteeing Subsidiary, on the one
                             hand, and the Holders and the Trustee, on the other
                             hand:

                             (i)  the maturity of the obligations guaranteed
                                  hereby may be accelerated as provided in
                                  Article 6 of the Indenture for the purposes of
                                  the Subsidiary Guarantee made pursuant to this
                                  Supplemental Indenture, notwithstanding any
                                  stay, injunction or other prohibition
                                  preventing such acceleration in respect of the
                                  obligations guaranteed hereby; and

                             (ii) in the event of any declaration of
                                  acceleration of such obligations as provided
                                  in Article 6 of the Indenture, such
                                  obligations (whether or not due and payable)
                                  shall forthwith become due and payable by such
                                  Guaranteeing Subsidiary for the purpose of the
                                  Subsidiary Guarantee made pursuant to this
                                  Supplemental Indenture.

                        (i)  Each Guaranteeing Subsidiary shall have the right
                             to seek contribution from any other non-paying
                             Guaranteeing Subsidiary so long as the exercise of
                             such right does not impair the rights of the
                             Holders or the Trustee under the Subsidiary
                             Guarantee made pursuant to this Supplemental
                             Indenture.


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                                                                               5

                  4.    GUARANTEEING SUBSIDIARIES MAY CONSOLIDATE, ETC. ON
                        CERTAIN TERMS.

                        (a)  Except as set forth in Articles 4 and 5 of the
                             Indenture, nothing contained in the Indenture, this
                             Supplemental Indenture or in the Notes shall
                             prevent any consolidation or merger of any
                             Guaranteeing Subsidiary with or into the Company or
                             any other Guarantor or shall prevent any transfer,
                             sale or conveyance of the property of any
                             Guaranteeing Subsidiary as an entirety or
                             substantially as an entirety, to the Company or any
                             other Guarantor.

                        (b)  Except as set forth in Article 4 of the Indenture,
                             nothing contained in the Indenture, this
                             Supplemental Indenture or in the Notes shall
                             prevent any consolidation or merger of any
                             Guaranteeing Subsidiary with or into a corporation
                             or corporations other than the Company or any other
                             Guarantor (in each case, whether or not affiliated
                             with such Guaranteeing Subsidiary), or successive
                             consolidations or mergers in which a Guaranteeing
                             Subsidiary or its successor or successors shall be
                             a party or parties, or shall prevent any sale or
                             conveyance of the property of any Guaranteeing
                             Subsidiary as an entirety or substantially as an
                             entirety, to a corporation other than the Company
                             or any other Guarantor (in each case, whether or
                             not affiliated with such Guaranteeing Subsidiary)
                             authorized to acquire and operate the same;
                             provided, however, that each Guaranteeing
                             Subsidiary hereby covenants and agrees that (i)
                             subject to the Indenture, upon any such
                             consolidation, merger, sale or conveyance, the due
                             and punctual performance and observance of all of
                             the covenants and conditions of the Indenture and
                             this Supplemental Indenture to be performed by such
                             Guaranteeing Subsidiary, shall be expressly assumed
                             (in the event that such Guaranteeing Subsidiary is
                             not the surviving corporation in the merger), by
                             supplemental indenture satisfactory in form to the
                             Trustee, executed and delivered to the Trustee, by
                             the corporation formed by such consolidation, or
                             into which such Guaranteeing Subsidiary shall have
                             been merged, or by the corporation which shall have
                             acquired such property and (ii) immediately after
                             giving effect to such consolidation, merger, sale
                             or conveyance no Default or Event of Default
                             exists.

                        (c)  In case of any such consolidation, merger, sale or
                             conveyance and upon the assumption by the successor
                             corporation, by supplemental indenture, executed
                             and delivered to the Trustee and satisfactory in
                             form to the Trustee, of the Subsidiary Guarantee
                             made pursuant to this Supplemental Indenture and
                             the due and punctual performance of all of the
                             covenants and conditions of the Indenture and this
                             Supplemental Indenture to be performed by


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                                                                               6

                             each Guaranteeing Subsidiary, such successor
                             corporation shall succeed to and be substituted for
                             such Guaranteeing Subsidiary with the same effect
                             as if it had been named herein as the Guaranteeing
                             Subsidiary. Such successor corporation thereupon
                             may cause to be signed any or all of the Subsidiary
                             Guarantees to be endorsed upon the Notes issuable
                             under the Indenture which theretofore shall not
                             have been signed by the Company and delivered to
                             the Trustee. All the Subsidiary Guarantees so
                             issued shall in all respects have the same legal
                             rank and benefit under the Indenture and this
                             Supplemental Indenture as the Subsidiary Guarantees
                             theretofore and thereafter issued in accordance
                             with the terms of the Indenture and this
                             Supplemental Indenture as though all of such
                             Subsidiary Guarantees had been issued at the date
                             of the execution hereof.

                  5.    RELEASES.

                        (a)  Concurrently with any sale of assets (including, if
                             applicable, all of the Capital Stock of a
                             Guaranteeing Subsidiary), all Liens, if any, in
                             favor of the Trustee in the assets sold thereby
                             shall be released; provided that in the event of an
                             Asset Sale, the Net Proceeds from such sale or
                             other disposition are treated in accordance with
                             the provisions of Section 4.10 of the Indenture. If
                             the assets sold in such sale or other disposition
                             include all or substantially all of the assets of a
                             Guaranteeing Subsidiary or all of the Capital Stock
                             of a Guaranteeing Subsidiary, then the Guaranteeing
                             Subsidiary (in the event of a sale or other
                             disposition of all of the Capital Stock of such
                             Guaranteeing Subsidiary) or the Person acquiring
                             the property (in the event of a sale or other
                             disposition of all or substantially all of the
                             assets of such Guaranteeing Subsidiary) shall be
                             released from and relieved of its obligations under
                             this Supplemental Indenture and its Subsidiary
                             Guarantee made pursuant hereto; provided that in
                             the event of an Asset Sale, the Net Proceeds from
                             such sale or other disposition are treated in
                             accordance with the provisions of Section 4.10 of
                             the Indenture. Upon delivery by the Company to the
                             Trustee of an Officers' Certificate to the effect
                             that such sale or other disposition was made by the
                             Company or the Guaranteeing Subsidiary, as the case
                             may be, in accordance with the provisions of the
                             Indenture and this Supplemental Indenture,
                             including without limitation, Section 4.10 of the
                             Indenture, the Trustee shall execute any documents
                             reasonably required in order to evidence the
                             release of the Guaranteeing Subsidiary from its
                             obligations under this Supplemental Indenture and
                             its Subsidiary Guarantee made pursuant hereto. If
                             the Guaranteeing Subsidiary is not released from
                             its obligations under its Subsidiary Guarantee, it
                             shall remain liable for the full amount of
                             principal of and interest on the Notes and for the
                             other

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                                                                               7


                             obligations of such Guaranteeing Subsidiary under
                             the Indenture as provided in this Supplemental
                             Indenture.

                        (b)  Upon the designation of a Guaranteeing Subsidiary
                             as an Unrestricted Subsidiary in accordance with
                             the terms of the Indenture, such Guaranteeing
                             Subsidiary shall be released and relieved of its
                             obligations under its Subsidiary Guarantee and this
                             Supplemental Indenture. Upon delivery by the
                             Company to the Trustee of an Officers' Certificate
                             and an Opinion of Counsel to the effect that such
                             designation of such Guaranteeing Subsidiary as an
                             Unrestricted Subsidiary was made by the Company in
                             accordance with the provisions of the Indenture,
                             including without limitation Section 4.07 of the
                             Indenture, the Trustee shall execute any documents
                             reasonably required in order to evidence the
                             release of such Guaranteeing Subsidiary from its
                             obligations under its Subsidiary Guarantee. Any
                             Guaranteeing Subsidiary not released from its
                             obligations under its Subsidiary Guarantee shall
                             remain liable for the full amount of principal of
                             and interest on the Notes and for the other
                             obligations of any Guaranteeing Subsidiary under
                             the Indenture as provided herein.

                  6.    NO RECOURSE AGAINST OTHERS. No past, present or future
director, officer, employee, incorporator, stockholder or agent of any
Guaranteeing Subsidiary, as such, shall have any liability for any obligations
of the Company or any Guaranteeing Subsidiary under the Notes, any Subsidiary
Guarantees, the Indenture or this Supplemental Indenture or for any claim based
on, in respect of, or by reason of, such obligations or their creation. Each
Holder of the Notes by accepting a Note waives and releases all such liability.
The waiver and release are part of the consideration for issuance of the Notes.
Such waiver may not be effective to waive liabilities under the federal
securities laws and it is the view of the Commission that such a waiver is
against public policy.

                  7.    SUBORDINATION OF SUBSIDIARY GUARANTEES; ANTI-LAYERING.
No Guaranteeing Subsidiary shall incur, create, issue, assume, guarantee or
otherwise become liable for any Indebtedness that is subordinate or junior in
right of payment to any Senior Debt of a Guaranteeing Subsidiary and senior in
any respect in right of payment to any of the Subsidiary Guarantees.
Notwithstanding the foregoing sentence, the Subsidiary Guarantee of each
Guaranteeing Subsidiary shall be subordinated to the prior payment in full of
all Senior Debt of that Guaranteeing Subsidiary (in the same manner and to the
same extent that the Notes are subordinated to Senior Debt), which shall include
all guarantees of Senior Debt.

                  8.    THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY, AND
CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK.

                  9.    COUNTERPARTS. The parties may sign any number of copies
of this Supplemental Indenture. Each signed copy shall be an original, but all
of them together represent the same agreement.


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                                                                               8

                  10.   EFFECT OF HEADINGS. The Section headings herein are for
convenience only and shall not affect the construction hereof.

                  11.   THE TRUSTEE. The Trustee shall not be responsible in any
manner whatsoever for or in respect of the validity or sufficiency of this
Supplemental Indenture or for or in respect of the recitals contained herein,
all of which recitals are made solely by the Guaranteeing Subsidiaries and the
Company.




















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                  IN WITNESS WHEREOF, the parties hereto have caused this
Supplemental Indenture to be duly executed and attested, all as of the date
first above written.



Dated: March 10, 2003        L-3 COMMUNICATIONS CORPORATION


                             By: /s/ Christopher C. Cambria
                                 ------------------------------------
                                 Name:
                                 Title:


























<PAGE>


Dated: March 10, 2003        AMI INSTRUMENTS, INC.
                             APCOM, INC.
                             BROADCAST SPORTS INC.
                             CELERITY SYSTEMS INCORPORATED
                             EER SYSTEMS, INC.
                             ELECTRODYNAMICS, INC.
                             HENSCHEL INC.
                             HYGIENETICS ENVIRONMENTAL SERVICES, INC.
                             INTERSTATE ELECTRONICS CORPORATION
                             KDI PRECISION PRODUCTS, INC.
                             L-3 COMMUNICATIONS AIS GP CORPORATION
                             L-3 COMMUNICATIONS ANALYTICS CORPORATION
                             L-3 COMMUNICATIONS ATLANTIC SCIENCE AND TECHNOLOGY
                                     CORPORATION
                             L-3 COMMUNICATIONS AYDIN CORPORATION
                             L-3 COMMUNICATIONS ESSCO, INC.
                             L-3 COMMUNICATIONS ILEX SYSTEMS, INC.
                             L-3 COMMUNICATIONS IMC CORPORATION
                             L-3 COMMUNICATIONS INTEGRATED SYSTEMS L.P.
                             L-3 COMMUNICATIONS INVESTMENTS, INC.
                             L-3 COMMUNICATIONS SECURITY AND DETECTION SYSTEMS
                                     CORPORATION DELAWARE
                             L-3 COMMUNICATIONS SECURITY AND DETECTION SYSTEMS
                                     CORPORATION CALIFORNIA
                             L-3 COMMUNICATIONS SPD TECHNOLOGIES, INC.
                             L-3 COMMUNICATIONS STORM CONTROL    SYSTEMS, INC.
                             L-3 COMMUNICATIONS TMA CORPORATION
                             L-3 COMMUNICATIONS WESTWOOD CORPORATION
                             MCTI ACQUISITION CORPORATION
                             MICRODYNE COMMUNICATIONS TECHNOLOGIES INCORPORATED
                             MICRODYNE CORPORATION
                             MICRODYNE OUTSOURCING INCORPORATED
                             MPRI, INC.
                             PAC ORD INC.
                             POWER PARAGON, INC.
                             SHIP ANALYTICS, INC.
                             SHIP ANALYTICS INTERNATIONAL, INC.
                             SHIP ANALYTICS USA, INC.
                             SOUTHERN CALIFORNIA MICROWAVE, INC.


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                                                                               2


                             SPD ELECTRICAL SYSTEMS, INC.
                             SPD HOLDINGS, INC.
                             SPD SWITCHGEAR INC.
                             SYCOLEMAN CORPORATION
                             TELOS CORPORATION
                             TROLL TECHNOLOGY CORPORATION
                             WESCAM AIR OPS INC.
                             WESCAM AIR OPS LLC
                             WESCAM INCORPORATED
                             WESCAM LLC
                             WESCAM SONOMA INC.
                             WESCAM HOLDINGS (US) INC.
                             WOLF COACH, INC.
                                     As Guaranteeing Subsidiaries

                             By: /s/ Christopher C. Cambria
                                 -------------------------------------
                                 Name:
                                 Title:



















<PAGE>



Dated:  March 10, 2003       THE BANK OF NEW YORK,
                             as Trustee


                             By: /s/ Kisha A. Holder
                                 -----------------------------------
                                 Name: Kisha A. Holder
                                 Title: Assistant Treasurer