Adding a little-
The OED says that skivvy for undershirt is of unknown origin, but tends toward a Nautical origin (1987 supplement), possibly because the first written reference is to cutting away a sailor's undershirt to get at a wound (1932).
Skivvy, however, has come to mean underwear including the pants in the present-day U. S. Navy.
Robert Chapman in his Dictionary of American Slang says skivvy is of naval origin, referring to underwear.

Slavey has been used for a black boy servant in Australia ca. 1900 (OED).
In a Flash dictionary of 1812, slavey indicated a servant of either sex (OED).

A skivvy waver is a naval signalman (May be no older than WW2).