you know they do make mods like the los angeles attack sub, the typhoon SSBN with working missiles (unguided to an extent), and the yamato battleship to name a few. but you have to have the game patched to 1.5 or otherwise known as the uboat mission pack which contains this update i believe. to enable the mods use jgsme (jones soft generic mod enabler) and the mods are available on subsim.com
however a trainer would be nice.