Things aren't lookin' so hot for Margaret and her troops in the play's final battle. So, Margaret tries to rally the troops by giving them a fancy speech. She decides that her army is like a ship:
What though the mast be now blown overboard,
The cable broke, the holding-anchor lost,
And half our sailors swallowed in the flood?
Yet lives our pilot still. (5.4.3-6)
Okay, so the soldiers are a ship at sea, and that ship is having a rough time. Even though their anchor (Warwick) and topmast (Montague) are both gone, they still have another anchor (Oxford) and mast (Somerset) to keep them going, so there's no need to let the ruthless sea (Edward), quicksand (Clarence) and rocks (Richard) bring the ship down.
It's one of the few times we get any imagery of people truly working together. Most of the time, the characters are just in it for themselves.
Too bad this one doesn't work out: Margaret and her army are, of course, totally defeated in the end.