Ah, that joke always reminds me of the Detroit River Light at the south end of the Detroit River where it joins Lake Erie. I'm surprised Wikipedia doesn't tell the story - I'll have to fix that.

lighthouse.boatnerd.com says this:

The construction of the station was tested in December 1997 when the 635-foot freighter Buffalo struck the station dead on while sailing downbound for Lake Eire (sic). Damage to the station was minimal involving only the structure's rock and stone foundation.
The freighter faired (sic, sic, sic) much worse with its steel bow push in like a tin can. The station's stone pier torn a 25-foot gash across the bow of the freighter which then took on water. The vessel was able to control the flooding and continued on for repairs.

The Detroit River Light sustained more significant damage in 1979, when it was struck by the freighter Stephen B. Roman. When you see the Detroit River Light, you do wonder why they stuck a lighthouse in such a vulnerable location. Maybe there's a reef or island upstream, or maybe it's just meant to mark the entrance to the Detroit River.

-Joe-

P.S. The Navy denies the joke about the lighthouse and the Coral Sea.