This is from

Hugill, Stan. Shanties from the Seven Seas. London: Routledge & K. Paul, 1961, page 456.

This is a "limited preview" book at Google Book Search, and the page previous to this one is not available for viewing, so I can't give much background to the song. However, it says

...sent in by Mr. Neil H. Wilson of North Tonawonda, New York.

OLD ENGLISH CHANTEY

A's for the Anchor that hangs o'er our bow
B's for the Bowsprit, as everyone knows;
C's for the Capstan we merrily walk around,
D's for the Davits which lower our boat down.

CHORUS: So merry, so merry, so merry are we,
No mortals on earth are like sailors at sea.
Hi derry, ho derry, hey derry down,
Give sailors their grog and there's nothing goes wrong.

E's for the Ensign which at our peak flew,
F's for the Fo'castle where live all our crew,
G's for the Guns where our brave boys did stand,
H's for the Hawsers, that never will strand.

I's for the Irons where our booms ship;
J's for the Jibs that so neatly do sit;
K's for the Keelson, of which we are told;
L's for the Lanyard that keeps a good hold.

M's for the Mainmast so stout and so strong;
N's for the Needle that never points wrong;
O's for the Oars of our jolly-boat;
P's for the Pinnace that always will float.

Q's for the Quarterdeck, where our officers stand;
R's for the Rudder, keeps the ship in command;
S's for the Stuns'ls that drive her along;
T's for the Topsails we hoist with a song.

U's for the Union which we all adore;
V's for the Vane which flies at our fore,
W's for the Wheel at which we stand our time,
And the other three letters you can't bring in rhyme.

(By permission of Popular Publications Inc., New York)

This version I should say is very old and savours of the Navy. The reference to the Union (of England and Scotland) points to fair antiquity!