The Beatles Yellow Submarine wedding cake was created by deviantART user ~estranged-illusions. The cake was inspired by the 1968 animated Beatles movie, and apparently made for the coolest couple ever.
According to the cake artist:
Vanilla strawberry cake with strawberry filling, white buttercream and marshmallow fondant. The figures are all colour flow, with the exception of the submarine topper with the bride and groom on top. I made the topper from Sculpey so that they would have a keepsake.