Defense companies, which have suffered mightily on the stock markets of late, took a sharp upturn, led by General Dynamics Corp., which posted strong earnings last Wednesday and was upgraded by brokerage SG Cowen Thursday. Shares of General Dynamics, builder of the Seawolf submarine and M-1 tank, as well as Gulfstream corporate jets, gained as much as 5-1/8 in morning trading on the New York Stock Exchange, before settling back to 55-3/4, up 3-3/4. Exchange. A spate of aerospace- and defense-related companies posted earnings that mostly beat Wall Street expectations Wednesday, including commercial aircraft and defense giant Boeing Co. and United Technologies Corp., which makes engines and helicopters, but also elevators and air conditioning systems.