Sink the Bismarck

Lyrics:
In May of nineteen forty-one the war had just begun
The Germans had the biggest ship that had the biggest guns
The Bismark was the fastest ship that ever sailed the seas
On her deck were guns as big as steers and shells as big as trees
Out of the cold and foggy night came the British ship the Hood
And evry British seaman, he knew and understood
They had to sink the Bismark, the terror of the sea
Stop those guns as big as steers and those shells as big as trees
We'll find that German battleship thats makin' such a fuss
We gotta sink the Bismark 'cause the world depends on us
Hit the decks a-runnin' boys and spin those guns around
When we find the Bismark we gotta cut her down

Surely, though, that should be  "On her deck were shells as big as steers and guns as big as trees"?
(Most) trees are larger than steers, all guns are bigger than shells.