<PAGE>
                                                                    EXHIBIT 12 

                        L-3 COMMUNICATIONS CORPORATION 
              COMPUTATION OF RATIO OF EARNINGS TO FIXED CHARGES 
                    (IN THOUSANDS, EXCEPT FOR RATIO DATA) 

   
<TABLE>
<CAPTION>
                                         COMPANY 
                                     -------------- 
                         PRO FORMA     NINE MONTHS 
                        YEAR ENDED        ENDED 
                       DECEMBER 31,    DECEMBER 31, 
                           1997            1997 
                       -------------- -------------- 
<S>                   <C>            <C>
Earnings: 
 Income before 
  income taxes.......     $15,900        $22,992 
Add: 
 Interest expense ...      42,400         29,884 
 Interest component 
  of rent expense ...       5,133          3,445 
                      -------------- -------------- 
Earnings.............     $63,433        $56,321 
                      ============== ============== 
Fixed Charges: 
 Interest expense ...     $42,400        $29,884 
 Interest component 
  of rent expense ...       5,133          3,445 
                      -------------- -------------- 
Fixed Charges........     $47,533        $33,329 
                      ============== ============== 
Ratio of earnings to 
 fixed charges.......         1.3x           1.7x 
                      ============== ============== 
</TABLE>
    

                    (RESTUBBED TABLE CONTINUED FROM ABOVE) 

   
<TABLE>
<CAPTION>
                                                  PREDECESSOR COMPANY 
                      ---------------------------------------------------------------------------- 
                       THREE MONTHS                                   NINE MONTHS    THREE MONTHS 
                            ENDED        YEARS ENDED DECEMBER 31,         ENDED          ENDED 
                         MARCH 31,   ------------------------------  DECEMBER 31,     MARCH 31, 
                           1997         1996      1995      1994         1993            1993 
                       -------------- ---------  -------- ---------  -------------- -------------- 
<S>                   <C>            <C>        <C>      <C>        <C>            <C>              
Earnings: 
 Income before 
  income taxes.......     $ (505)      $19,494   $  174    $ 2,929      $ 8,300         $5,100 
Add: 
 Interest expense ...      8,441        24,197    4,475      5,450        4,100             -- 
 Interest component 
  of rent expense ...        851         2,832    1,591      1,866        1,400            467 
                      -------------- ---------  -------- ---------  -------------- -------------- 
Earnings.............     $8,787       $46,523   $6,240    $10,245      $13,800         $5,567 
                      ============== =========  ======== =========  ============== ============== 
Fixed Charges: 
 Interest expense ...     $8,441       $24,197   $4,475    $ 5,450      $ 4,100             -- 
 Interest component 
  of rent expense ...        851         2,832    1,591      1,866        1,400            467 
                      -------------- ---------  -------- ---------  -------------- -------------- 
Fixed Charges........     $9,292       $27,029   $6,066    $ 7,316      $ 5,500         $  467 
                      ============== =========  ======== =========  ============== ============== 
Ratio of earnings to 
 fixed charges.......         --(a)        1.7x     1.0x       1.4x         2.5x          n.a. 
                      ============== =========  ======== =========  ============== ============== 
</TABLE>
    

   
------------ 
(a)    Earnings were insufficient to cover fixed charges by $0.5 million for 
       the three months ended March 31, 1997.