Long, Hard, and Full of Seamen

Okay, so listen up, you chucklehead. The joke is playing on the double meaning of "seamen." Usually it's sailors, right? But, uh, it also sounds like "semen." And submarines are long and hard, like... well, you get it. Sheesh, I have to explain everything to you, don't I? By the way, scientists say that your brain is getting smaller. So sad!