Woooha....I could "unbury" hundreds of links I found when doing the research for the Pacific Aces mod
...but here are the more important ones for starters:
www.navsource.org TONS of pictures from real US war ships, nearly all are here together with emblems
www.valoratsea.com Hondo's web with lots of great stuff.
http://www.fleetsubmarine.com/ All you ever wanted to know about the fleet subs
http://www.maritime.org/fleetsub/index.htm The Fleet Submarine Manual on line. The REAL thing!