U.S. basic training has a rhyme "This is my weapon, this is my gun, one is for killing, one is for fun." "Gun"here = "penis".

In the military, "gun" officially means artillery pieces, I think, not smallarms.

The old version of the OED I have, however, says (following Skeat) that the English word "gun" may derive from the Norse woman's name Gunhilda given to an ancient artillery piece -- or else from a compound of "gun" + "hilde", approximately, both of which have martial meanings. (The second explanation ruins the joke, and I will ignore it.)

In far-fetched corroboration of this, there is a Swedish businesswoman here in Portland whose first name is Gun. I have not found out whether she blows shit up or not, but a woman I know who worked for her says that she's a good boss. The Scandinavians seem to have lost a lot of their oomph during the second millenium.

I believe in that rhyme "weapon" would be penis, and "gun" would be gun. Why wouldn't that be the case?

Begin's uncertain grasp of spoken Hebrew is on record, but I have doubts about this story, because at the time (1951) his son was nine years old.

What does his son's age have to do with it?

I always heard "This is my rifle, this is my gun..."

In the late 1960s and early 1970s, when I was in the U.S. Army, the rhyme was definitely the one that Steve cites. Referring to an M-14 as a "gun" was punished by 25 push-ups in basic training.

No one ever told us the reason.

And I don't remember anyone ever using "gun" for "penis", either, except in the context of that rhyme.

I heard "weapon" second hand. That was definitely it, though. Perhaps there were regional variants.

According to the Internet Movie Database, the rhyme as used in Full Metal Jacket is:

Gunnery Sergeant Hartman: [Chanting] This is my rifle.
Gunnery Sergeant Hartman: [Grabbing their crotches] This is my gun.
Marines: This is for fighting.
Marines: [Grabbing their crotches] This is for fun.

(Movable Type reckons that "db. com" is "questionable content", so I'm afraid you'll have to look it up for yourself.)

Oh dear. I'll take that one off the blacklist. I've been erring on the kill-em-all side in order to cut down the floods of spam, but banning IMDb is ridiculous. The quote is a great find!

That's a great story you linked to, Hat! But imprecise in its terminology (hey, where can I quibble if not here?). Some clarification:
zayen (זיין, for those of you following along at home) does mean "to arm," but not in Biblical Hebrew. If Begin was speaking Biblical Hebrew in 1952 I would be very astonished! (Whether anyone ever spoke Biblical Hebrew as such, well, that's another question which I would be happy to speculate about except that I'm not really qualified.) Surely he was speaking a high register of literary Hebrew, heavily influenced by Loshn-koydesh, the learned language of traditional Jews.

As an aside, the word for "male sexual member" (are we calling it that because there are ladies in the room?) in Biblical Hebrew proper seems to be something else: yerekh (ירך), sometimes translated over-literally as "thigh." When Abraham swears his servant Eliezer that he will only fetch the proper mate for his son, he says "Now put your hand under my yerekh". (Shades of "testify.")

Whoops. I meant to write that Father Abraham made Eliezer swear, etc.

Oh, crap. I just saw your intro to the post, Steve, and of course you called the register in question by an appropriate name. I'm sorry. I should have no further interaction with human beings until I finish revising my dissertation.

*shuts airlock*

*bangs on airlock*
Come out of there! I was wondering what the actual words in question were, and you've answered my unasked question -- don't vanish into the dungeon of your dissertation! (Of course, you don't want to wind up ABD like me, so you probably shouldn't listen to me...)

Oh, no no no - right when it gets to the juicy [sorry] parts!
Teaser.