Originally Posted by The Other Owner
The Poseidon is a missile (not a sub) designation. A "Poseidon submarine," an inaccurate colloquial usage, refers to the weapons complement, so it's a sub that carries Poseidon missiles. Not Tridents.
But that's just the geeky part. The funny part is that Tridents and Poseidons, like all SLBMs, are small, short and compact little guys. They don't get very big or long. Even when encouraged to do so. They are the shrimpy little cousins of the ICBM.
"Wanna check out my Trident?" Hilarious.;)