Green’s Dictionary of Slang

naval depot n.

the stomach.

1832		Egan Bk of Sports 158: His left [hand], stiff and straight, pointed smack at his opponent’s naval depôt.
c.1864		‘The Royal Passage’ in Rakish Rhymer (1917) 58: Let’s shout until we’re hoarse, / ‘Here’s the Queen’s Naval Department,’ and all under it, of course.