<PAGE>   1
                                                                      Exhibit 99

                            TRW Inc. and Subsidiaries
                        Computation of Ratio of Earnings
                          to Fixed Charges - Unaudited

                         (In millions except ratio data)

<TABLE>
<CAPTION>

                                                               Years Ended December 31
                                Nine Months
                                  ended          -------------------------------------------------------
                           September 30, 1998    1997           1996         1995       1994        1993
                           ------------------    ----           ----         ----       ----        ----

<S>                                <C>         <C>            <C>           <C>        <C>         <C>
Earnings from continuing
  operations before income
  taxes                            $566.0      $239.7(A)      $302.2(B)     $625.5     $435.5      $289.2

Unconsolidated affiliates            (0.1)       (8.0)           1.4           1.3       (0.6)        0.7

Minority earnings                     9.3        20.2           11.5          10.8        7.7         1.4

Fixed charges excluding
  capitalized interest              145.1       123.9          129.0         137.2      145.3       177.5
                                   ------      ------         ------        ------     ------      ------

Earnings                           $720.3      $375.8         $444.1        $774.8     $587.9      $468.8
                                   ------      ------         ------        ------     ------      ------

Fixed Charges:
Interest expense                   $100.5      $ 75.4         $ 84.2        $ 94.7     $104.7      $137.4

Capitalized interest                  2.4         4.5            3.5           5.1        6.6         7.9

Portion of rents representa-
  tive of interest factor            44.6        48.5           43.2          41.4       39.2        37.9

Interest expense of uncon-
  solidated affiliates                0.0         0.0            1.6           1.1        1.4         2.2
                                   ------      ------         ------        ------     ------      ------

Total fixed charges                $147.5      $128.4         $132.5        $142.3     $151.9      $185.4
                                   ------      ------         ------        ------     ------      ------

Ratio of earnings to fixed            4.9x        2.9x           3.4x          5.4x       3.9x        2.5x
  charges                          -------     -------        -------       -------    -------     -------
</TABLE>




(A)  The 1997 earnings from continuing operations before income taxes of 
     $239.7 million includes a $548 million earnings charge for purchased 
     in-process research and development. See "Acquisitions" footnote in the 
     Notes to Financial Statements of the Company's 1997 Annual Report to 
     Shareholders.

(B)  The 1996 earnings from continuing operations before income taxes of 
     $302.2 million includes a charge of $384.8 million as a result of actions 
     taken in the automotive and space and defense businesses. See 
     "Divestiture and special charges" footnote in the Notes to Financial 
     Statements of the Company's 1996 Annual Report to Shareholders.