What is 2 if by sea?

Answer 1

"One if by land. Two if by sea." This phrase gained its fame at the start of the American Revolution. The infamous Sons of Liberty had been smuggling amunition to a location in Concord, north of Boston in preparation for war with the British.

The Sons of Liberty new that the British were on to them and were planning to raid the Patriot stash in Concord, so they were spying on the Red Coats to let the Patriots north of Boston know how the British troops would travel.

In the tower of the Old North Church, the Patriots would place a one lantern if the troops were marching out of Boston. They would place two laterns if the troops climbed aboard boats to cross the harbor and start their march at Cambridge toward Concord.

The British did indeed take the sea route...and thus the famous phrase.