<PAGE>   1
                                                                 EXECUTION COPY

                                                               EXHIBIT 10.01-05


                                            FOURTH AMENDMENT dated as of April
                                    30, 1999 (this "Fourth Amendment"), to the
                                    Amended and Restated Credit Agreement dated
                                    as of October 15, 1997, (as amended by the
                                    First Amendment dated as of June 26, 1998
                                    (the "First Amendment"), the Second
                                    Amendment dated as of November 13, 1998
                                    (the "Second Amendment") and the Third
                                    Amendment dated as of March 31, 1999 (the
                                    "Third Amendment"), and said Amended and
                                    Restated Credit Agreement as so amended
                                    being the "Credit Agreement"), among
                                    Firearms Training Systems, Inc., as Parent
                                    (the "Parent"), FATS, Inc., as Borrower
                                    (the "Borrower"), the lenders listed on the
                                    signature pages thereto (the "Lenders"),
                                    NationsBank, N.A., as Agent, (in such
                                    capacity, the "Agent"), Swingline Lender
                                    and Issuing Bank.

      The parties hereto have agreed, subject to the terms and conditions
hereof, to further amend the Credit Agreement as provided herein.

      Capitalized terms used and not otherwise defined herein shall have the
meanings assigned to such terms in the Credit Agreement (the Credit Agreement,
as amended by, and together with, this Fourth Amendment, and as hereinafter
amended, modified, extended or restated from time to time, being called the
"Amended Agreement").

      Accordingly, the parties hereto hereby agree as follows:

      SECTION 1.01. Amendment to Article V. Article V of the Credit Agreement
is hereby amended by inserting the following after the end of Section 5.15:

            "SECTION 5.16. Fourth Amendment Fee. On the earlier of (a) May 31,
      1999 and (b) the collection of a receivable from the Italian Air Force
      III "Italian Military Authorities Purchase Order No. 11/3443-II/4653/2"
      (which receivable is valued at $4,782,810), the Borrower shall pay to the
      Agent for the ratable benefit of the Lenders a fee equal to 0.25% of the
      total Commitments existing as of April 30, 1999 (after the reduction of
      the Revolving Credit Commitments as set forth in Section 2.10(f) hereof),
      as consideration for the Lenders' agreements as set forth in the Fourth
      Amendment dated as of April 30, 1999 to this Amended Agreement."

      SECTION 1.02. Amendment to Section 6.15. (a) Section 6.15(a) of the
Credit Agreement is hereby amended by deleting the chart therefrom in its
entirety and substituting in lieu thereof the following:

<TABLE>
<CAPTION>
      "From and including           To and including                 Ratio
      -------------------           ----------------                 -----
      <S>                          <C>                           <C>
      The Effective Date           December 31, 1997             1.75 to 1.00
</TABLE>
<PAGE>   2

<TABLE>
      <S>                          <C>                           <C>
      January 1, 1998              June 30, 1998                 2.10 to 1.00
      July 1, 1998                 September 30, 1998            1.55 to 1.00
      October 1, 1998              December 31, 1998             1.03 to 1.00
      January 1, 1999              March 31, 1999                0.80 to 1.00
      April 1, 1999                June 30, 1999                 1.10 to 1.00
      July 1, 1999                 September 30, 1999            1.40 to 1.00
      October 1, 1999              December 31, 1999             1.95 to 1.00
      January 1, 2000              March 31, 2000                2.38 to 1.00
      April 1, 2000                December 31, 2000             2.60 to 1.00
      January 1, 2001              December 31, 2001             2.95 to 1.00
      January 1, 2002              December 31, 2002             3.40 to 1.00
      January 1, 2003              June 30, 2003                 4.00 to 1.00"
</TABLE>

      (b) Section 6.15(b) of the Credit Agreement is hereby amended by deleting
therefrom the chart in its entirety and substituting in lieu thereof the
following:

<TABLE>
<CAPTION>
      "From and including           To and including                 Ratio
      -------------------           ----------------                 -----
      <S>                          <C>                           <C>
      The Effective Date           December 31, 1997             1.30 to 1.00
      January 1, 1998              June 30, 1998                 1.35 to 1.00
      July 1, 1998                 September 30, 1998            0.75 to 1.00
      October 1, 1998              December 31, 1998             0.41 to 1.00
      January 1, 1999              March 31, 1999                0.30 to 1.00
      April 1, 1999                June 30, 1999                 0.38 to 1.00
      July 1, 1999                 September 30, 1999            0.52 to 1.00
      October 1, 1999              December 31, 1999             0.83 to 1.00
      January 1, 2000              March 31, 2000                1.01 to 1.00
      April 1, 2000                December 31, 2000             1.40 to 1.00
      January 1, 2001              June 30, 2003                 1.50 to 1.00"
</TABLE>

      (c) Section 6.15(c) of the Credit Agreement is hereby amended by deleting
the chart therefrom in its entirety and substituting in lieu thereof the
following:



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<PAGE>   3

<TABLE>
<CAPTION>
      "From and including           To and including                Ratio
      -------------------           ----------------                -----
      <S>                          <C>                           <C>
      The Effective Date           December 31, 1997             4.80 to 1.00
      January 1, 1998              March 31, 1998                4.00 to 1.00
      April 1, 1998                June 30, 1998                 5.50 to 1.00
      July 1, 1998                 September 30, 1998            8.20 to 1.00
      October 1, 1998              December 31, 1998             12.13 to 1.00
      January 1, 1999              March 31, 1999                13.56 to 1.00
      April 1, 1999                June 30, 1999                 9.41 to 1.00
      July 1, 1999                 September 30, 1999            7.15 to 1.00
      October 1, 1999              December 31, 1999             5.10 to 1.00
      January 1, 2000              March 31, 2000                4.30 to 1.00
      April 1, 2000                December 31, 2000             3.10 to 1.00
      January 1, 2001              December 31, 2001             2.75 to 1.00
      January 1, 2002              June 30, 2003                 2.25 to 1.00"
</TABLE>

      SECTION 1.03. Representations and Warranties. The Borrower hereby
represents and warrants to the Agents and the Lenders, as follows:

            (a) The representations and warranties set forth in Article III of
      the Amended Agreement, and in each other Loan Document, including any
      Schedules thereto, are true and correct in all material respects on and
      as of the date hereof and on and as of the Fourth Amendment Effective
      Date (as defined below) with the same effect as if made on and as of the
      date hereof or the Fourth Amendment Effective Date, as the case may be,
      except to the extent such representations and warranties expressly relate
      solely to an earlier date.

            (b) Each of the Borrower and the other Loan Parties is in
      compliance with all the terms and conditions of the Amended Agreement and
      the other Loan Documents on its part to be observed or performed and no
      Default or Event of Default has occurred or is continuing under the
      Amended Agreement.

            (c) The execution, delivery and performance by the Borrower of this
      Fourth Amendment have been duly authorized by the Borrower.

            (d) This Fourth Amendment constitutes the legal, valid and binding
      obligation of the Borrower, enforceable against the Borrower in
      accordance with its terms.

            (e) The execution, delivery and performance by the Borrower of this
      Fourth Amendment (i) does not conflict with or violate (A) any provision
      of law, statute, rule or regulation, or of the articles of incorporation
      or by-laws of the Borrower, (B) any order of any Governmental Authority
      or (C) any provision of any indenture, agreement or other instrument to
      which the Borrower is a party or by which it or any of its property may
      be bound and (ii) does not require any consents under, result in a breach
      of or constitute (alone or with notice or lapse of time or both) a
      default or give rise to increased, additional, accelerated or guaranteed
      rights of any person under any such indenture, agreement or instrument.



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<PAGE>   4

      SECTION 1.04. Effectiveness. This Fourth Amendment shall be deemed
effective as of April 30, 1999 only upon satisfaction of the following
conditions precedent (the first date upon which each such condition has been
satisfied being herein called the "Fourth Amendment Effective Date"):

            (a) The Agent shall have received duly executed counterparts of
      this Fourth Amendment which, when taken together, bear the authorized
      signatures of the Parent, the Borrower and the Required Lenders.

            (b) The Lenders shall be satisfied that the representations and
      warranties set forth in Section 1.03 hereof are true and correct on and
      as of the Fourth Amendment Effective Date.

            (c) There shall not be any action pending or any judgment, order or
      decree in effect which, in the judgment of the Lenders or their counsel,
      is likely to restrain, prevent or impose materially adverse conditions
      upon performance by the Borrower or any other Loan Party of its
      obligations under the Loan Documents.

            (d) The Lenders shall have received such other documents, legal
      opinions, instruments and certificates as they shall reasonably request
      and such other documents, legal opinions, instruments and certificates
      shall be satisfactory in form and substance to the Lenders and their
      counsel. All corporate and other proceedings taken or to be taken in
      connection with this Fourth Amendment and all documents incidental
      thereto, whether or not referred to herein, shall be satisfactory in form
      and substance to the Lenders and their counsel.

            (e) The Agent shall have received payment of all fees and expenses
      set forth in Section 1.06.

      SECTION 1.05. APPLICABLE LAW. THIS FOURTH AMENDMENT SHALL BE GOVERNED BY,
AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK, EXCEPT TO
THE EXTENT THAT THE FEDERAL LAWS OF THE UNITED STATES OF AMERICA MAY APPLY.

      SECTION 1.06. Fees and Expenses. The Borrower shall pay all reasonable
out-of-pocket expenses incurred by the Agent and the Lenders in connection with
the preparation, negotiation, execution, delivery and enforcement of this
Fourth Amendment, including, but not limited to, the reasonable fees and
disbursements of counsel; provided, however that such amendment fee and such
expenses shall be excluded from the calculations of the covenants set forth in
Section 6.15 where applicable.

      SECTION 1.07 Reporting Requirements. (a) Each month, beginning with the
month ending April 30, 1999, the Borrower shall provide the Agent, for
distribution to the Lenders, with a monthly consolidated income statement,
balance sheet and cash flow statement. Such information


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<PAGE>   5

shall be provided to Agent no later than the 15th day of the month immediately
succeeding the month to which such information relates.

            (b) On Wednesday of each week, beginning with the week ending April
      30, 1999, the Borrower shall provide the Agent, for distribution to the
      Lenders, with an updated weekly cash flow forecast for the 26 succeeding
      calendar weeks.

      SECTION 1.08. Counterparts. This Fourth Amendment may be executed in any
number of counterparts, each of which shall constitute an original but all of
which when taken together shall constitute but one agreement.

      SECTION 1.09. Credit Agreement. Except as expressly set forth herein, the
amendments provided herein shall not by implication or otherwise limit,
constitute a waiver of, or otherwise affect the rights and remedies of the
Lenders, the Agent or the other Secured Parties under the Amended Agreement or
any other Loan Document, nor shall they constitute a waiver of any Default or
Event of Default, nor shall they alter, modify, amend or in any way affect any
of the terms, conditions, obligations, covenants or agreements contained in the
Amended Agreement or any other Loan Document. Each of the amendments provided
herein shall apply and be effective only with respect to the provisions of the
Amended Agreement specifically referred to by such amendment. Except as
expressly amended herein, the Amended Agreement shall continue in full force
and effect in accordance with the provisions thereof. As used in the Amended
Agreement, the terms "Agreement", "herein", "hereinafter", "hereunder",
"hereto" and words of similar import shall mean, from and after the date
hereof, the Amended Agreement.


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<PAGE>   6

         IN WITNESS WHEREOF, the parties hereto have caused this Fourth
Amendment to be duly executed by their duly authorized officers, all as of the
date first above written.

                            FIREARMS TRAINING SYSTEMS, INC.
                            as Parent


                            By:
                               -----------------------------------------------
                              Name:
                              Title:



                            FATS, INC.
                            as Borrower


                            By:
                               -----------------------------------------------
                              Name:
                              Title:



                            NATIONSBANK, N.A., as Agent, Swingline
Lender
                            and Issuing Bank and individually as a Lender


                            By:
                               -----------------------------------------------
                              Name:
                              Title:



                            U.S. BANK NATIONAL ASSOCIATION


                            By:
                               -----------------------------------------------
                              Name:
                              Title:



                            FIRST SOURCE FINANCIAL LLP, by First Source
                            Financial, Inc., as Agent/Manager


                            By:
                               -----------------------------------------------
                              Name:


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<PAGE>   7

                              Title:



                            BHF-BANK AKTIENGESELLSCHAFT


                            By:
                               -----------------------------------------------
                              Name:
                              Title



                            BANK AUSTRIA CREDITANSTALT
CORPORATE
                            FINANCE, INC. (FKA CREDITANSTALT
                            CORPORATE FINANCE, INC.)


                            By:
                               -----------------------------------------------
                              Name:
                              Title:


                            By:
                               -----------------------------------------------
                              Name:
                              Title:


         The undersigneds hereby agree and consent to each of the First
Amendment, Second Amendment, Third Amendment and Fourth Amendment as of the
respective dates of such amendments.

FIREARMS TRAINING SYSTEMS, INC.,
         as Guarantor


By:
   ------------------------
  Name:
  Title:



DART INTERNATIONAL, INC.,
  as Guarantor


By:
   ------------------------
  Name:
  Title:



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