Lockheed Martin tumbles on $1.6 billion Q2 charge

Shares of Lockheed Martin LMT.N fall 7% to ~$427 in premarket trading

Defense giant recorded charge of $1.6 billion in Q2, causing profit to plunge by about 80%

Says charge due to difficulties with classified program in aeronautics segment and on international helicopter programs in its Sikorsky unit

*Posted Q2 EPS of $1.46 vs. $6.85 per share last year

11 of 24 brokerages rate the stock "buy" or higher, 12 "hold" and one "sell"; their median PT is $527.5

Shares down 5.23% YTD