FOURTH MODIFICATION AGREEMENT TO STOCK PURCHASE AGREEMENT This Fourth Modification Agreement (the "Modification Agreement") is entered into as of September 30, 1999, by and between Engineered Systems and Electronics, Inc., a Missouri corporation...

                  FOURTH MODIFICATION AGREEMENT
                   TO STOCK PURCHASE AGREEMENT

  This   Fourth   Modification   Agreement   (the   "Modification
Agreement")  is  entered into as of September 30,  1999,  by  and
between Engineered Systems and Electronics, Inc.,
a   Missouri   corporation  ("Buyer"),   and   ESCO   Electronics
Corporation, a Missouri corporation ("ESCO"), and Defense Holding
Corp.,  a Delaware corporation ("DHC") (Buyer, ESCO and  DHC  are
sometimes hereinafter collectively referred to as the "Parties").

                            Recitals

  WHEREAS, the Parties have entered into the Stock Purchase
Agreement dated August 23, 1999 ("Stock Purchase Agreement"),
whereby Buyer agrees to purchase from Sellers, on the terms and
conditions set forth in the Stock Purchase Agreement, one
thousand (1,000) shares of the common stock, $1 par value per
share, of Systems & Electronics Inc., a Delaware corporation
which is a direct wholly-owned subsidiary of DHC and an indirect
wholly-owned subsidiary of ESCO;

  WHEREAS, the Parties desire to amend the Stock Purchase
Agreement as provided below; and

  WHEREAS, Engineered Support Systems, Inc. has executed a
joinder to the Stock Purchase Agreement as of the same date
thereof, and it acknowledges and agrees to the modification of
the Stock Purchase Agreement as set forth below.

  NOW, THEREFORE, the parties agree as follows:
     Attached hereto are certain revised Schedules and/or
     Exhibits to the Stock Purchase Agreement.  Each such revised
     Schedule and/or Exhibit attached hereto shall amend or
     replace, as specified in such revised Schedule and/or
     Exhibit, the corresponding numbered Schedule and/or Exhibit
     attached to the Stock Purchase Agreement.

  IN  WITNESS WHEREOF, each of the Parties hereto has caused this
Modification Agreement to be executed as of the date first  above
written.

ESCO:                            BUYER:
ESCO ELECTRONICS CORPORATION     ENGINEERED SYSTEMS AND
  Xxxxxx Xxxxx,                  ELECTRONICS, INC.
  Senior Vice President and        Xxxx X. Xxxxxxxx,
  General Counsel                  Executive Vice President and
                                   Chief Financial
                                   Officer
DHC:
DEFENSE HOLDING CORP.
  Xxxxxx Xxxxx,
  Senior Vice President and
  Secretary


                              JOINDER


The foregoing Modification Agreement is approved by the undersigned
and the undersigned hereby acknowledges and agrees this September
30, 1999 to such modification to the Stock Purchase Agreement and
joins therein.

ENGINEERED SUPPORT SYSTEMS,
INC.:
  Xxxx X. Xxxxxxxx,
  Executive Vice President and
  Chief
  Financial Officer