WordNet
n. a boat serving as a picket
Wikipedia
A picket boat is a type of small military craft. These are used for harbor patrol and other close inshore work, and have often been carried by larger warships as a ship's boat.
(In addition, patrol boats, or any craft engaged in sentinel duty, are sometimes referred to as picket boats, using "picket" in the generic sense, even if much larger than actual picket boats.)
Usage examples of "picket boat".
The Americans must have flown them off one of the carriers the picket boat had spotted.
He led a picket boat smaller than his present command into the harbor of the enemy and sank four ships and damaged a dozen others before his own boat was sunk under him.
If they were apprehended by a picket boat or were under fire by a blockading vessel, there would be no escape except by diving and waiting it out on the bottom.
I was inbound on a supply runIve been acting as supply sergeant for the picket boat.
All about them in space, tethered by snaking tie lines, other men were assembling boxes, Marines were fanning out, Navy techs were already assembling the parts of a picket boat.