IRL the MANPADS are really for when a submarine is transiting and could come under air attack (think terrorists flying a plane in to a nuclear sub to contaminate a waterway, or a sub surfaced though the ice to launch SLBMs).
Subs don't genneraly get "cought" snorkeling. They spend quite a bit of time (hours even days) before hand making sure the area is totaly clear, and will sneek in among any surface traffic before snorting.
Combat aircraft have a huge advantage over a surface submarine, even a fighter's cannon could do some serrious damage if its AP rounds pentrated the pressure hull. Yea you might shoot down a plane but now you can't dive because there are a couple hundred holes in your hull and more bad guys are on the way.
I think we can track down this whole submarine SAM issue to the Falklands where the ARA Santa Fe (an old GUPPY diesel) was caught on the surface by a couple of helos and got pounded. the sub crew fought back with rifles and Anti-Tank missiles (they had some commandoes on board) to no effect and beach the sub rather than be killed. Everyone looked at this and said "Hay lets get some AA missiles on our subs" not realizing that modern diesels can dive a heck of a lot longer than an old 1950's GUPPY. The Soviets being willing to try anything put a little SAM position in their sails that thanks to some novelists who didn't know what they were talking about or confused it with a one off British system for Israel suddonly became a underwater launch capable missile system for wasting waves of choppers. When in reality its a limited defensive weapon for a couple of rare situations. Heck submarines carry machine guns still but we don't have them in DW! I kinda agree with ML the SAMs are a feature that should have been included but made a little better, and a skilled airborne ASW player can make such a weapon worse than useless- a liablity.
__________________
 
|