Exhibit 4.13
 
  W I T N E S S E T H
       (a)
    
    Such 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,
interest and Additional Interest, if any, 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, interest and Additional
Interest, if any, 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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(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 such 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.
  (a)
    
    To evidence its Subsidiary Guarantee set forth
in this Supplemental Indenture, such 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, such
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 hereof or
thereof, the recovery of any judgment against the Company, any action
to enforce the same or any other 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
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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.
  (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 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
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with or into a corporation or corporations
other than the Company or any other Guarantor (in each case, whether or
not affiliated with the 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
the 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 Subsidiaries, 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 such 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.
  (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 (it
being understood that only such portion of the Net
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Proceeds as is
required to be applied on or before the date of such sale or other
disposition in accordance with the terms of the Indenture needs to be
applied in accordance therewith at such time). 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 (it being understood that only such
portion of the Net Proceeds as is required to be applied on or before
the date of such sale or other disposition in accordance with the
terms of the Indenture needs to be applied in accordance therewith at
such time). 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 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 or upon the release of a Guarantor from its Guarantees
of, and all pledges and security interests granted in connection with,
all other Indebtedness of the Company or any of their Restricted
Subsidiaries, 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.
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(c)
    
    Each Guaranteeing Subsidiary shall be released
and relieved of its obligations under this Supplemental Indenture in
accordance with, and subject to, Section 4.13 of the Indenture.
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Dated: February 20, 2009
    L-3 COMMUNICATIONS CORPORATIONBy:
    /s/ Steven M. PostName:
    Steven M. PostTitle:
    Senior Vice President, General Counsel and Corporate Secretary




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As Guaranteeing SubsidiariesBy:

/s/
Steven M. PostName:
    Steven M. PostTitle:
    Vice President and Secretary  By: L-3 COMMUNICATIONS AIS GP CORPORATION, as General PartnerBy:

/s/
Steven M. PostName:
    Steven M. PostTitle:
    Vice President and Secretary 
 By: L-3 COMMUNICATIONS VERTEX AEROSPACE LLC, as Sole MemberBy: L-3 COMMUNICATIONS INTEGRATED SYSTEMS L.P., as Sole MemberBy: L-3 COMMUNICATIONS AIS GP CORPORATION, as General PartnerBy:
    
    /s/
Steven M. PostName:
    
    Steven M. PostTitle:
    
    Vice President and Secretary
  By: L-3 COMMUNICATIONS INTEGRATED SYSTEMS L.P., as Sole MemberBy: L-3 COMMUNICATIONS AIS GP CORPORATION, as General PartnerBy:
    
    /s/
Steven M. PostName:
    
    Steven M. PostTitle:
    
    Vice President and Secretary




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By:
    L-3 COMMUNICATIONS CORPORATION, as Sole MemberBy:
    /s/
Steven M. PostName:
    Steven M. PostTitle:
    Senior Vice President, General Counsel and Corporate Secretary  By:
    L-3 COMMUNICATIONS CORPORATION, as Sole MemberBy:
    /s/
Steven M. PostName:
    Steven M. PostTitle:
    Senior Vice President, General Counsel and Corporate Secretary




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Dated:  February 20, 2009
    THE BANK OF NEW YORK MELLON,
as TrusteeBy:
    /s/ Franca FerreraName:
    Franca FerreraTitle:
    Assistant Vice President




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Supplemental Indenture Guarantor Guarantors Trustee




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As Guaranteeing SubsidiariesBy:
    /s/
Steven M. PostName:
    Steven M. PostTitle:
    Vice President and Secretary  By:  L-3 COMMUNICATIONS AIS GP CORPORATION, as General PartnerBy:
    /s/
Steven M. PostName:
    Steven M. PostTitle:
    Vice President and Secretary 
 By:                                          L-3 COMMUNICATIONS VERTEX AEROSPACE LLC, as Sole MemberBy:                                          L-3 COMMUNICATIONS INTEGRATED SYSTEMS L.P., as Sole MemberBy:                                         L-3 COMMUNICATIONS AIS GP CORPORATION, as General PartnerBy:
    /s/
Steven M. PostName:
    Steven M. PostTitle:
    Vice President and Secretary  By:                                          L-3 COMMUNICATIONS INTEGRATED SYSTEMS L.P., as Sole MemberBy:                                          L-3 COMMUNICATIONS AIS GP CORPORATION, as General PartnerBy:
    /s/
Steven M. PostName:
    Steven M. PostTitle:
    Vice President and Secretary 2




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By:                                          L-3 COMMUNICATIONS CORPORATION, as Sole MemberBy:
    /s/
Steven M. PostName:
    Steven M. PostTitle:
    Senior Vice President, General Counsel and Corporate Secretary  By:                                          L-3 COMMUNICATIONS CORPORATION, as Sole MemberBy:
    /s/
Steven M. PostName:
    Steven M. PostTitle:
    Senior Vice President, General Counsel and Corporate Secretary 3