USS N-3 (SS-55) was a N-class coastal defense submarine in commission in the United States Navy from 1917 to 1926.

She was on patrol in the Atlantic Ocean during the predawn hours of 23 July, lying on the surface while charging her batteries in calm, hazy weather with bright moonlight, when at 02:55 she suddenly sighted at a range of only 1,800 yards (1,650 m) one of the ships of a convoy of five troop transports which had departed New York City on 21 July carrying U.S troops to Europe.

The British armed transport Minnekahda, carrying 3,800 U.S. troops, soon also appeared, headed straight at N-3 and only about 200 yards (183 m) away.

As N-3 continued to flash the recognition signal by blinker light, N-3′s commanding officer hailed Minnekahda, calling out "Don't fire, this is an American submarine!"

At that instant, one of Minnekahda′s guns fired a 6-or-7.5-inch (152 or 191 mm) round (according to different sources), and the shell hit N-3 forward at the waterline, failing to explode but inflicting considerable damage and causing leaks.

N-3 had suffered no crew casualties, but Minnekahda′s unexploded shell was found in N-3′s forward superstructure, and N-3′s torpedo compartment was partially flooded.

[1] Following permanent repairs at the New York Navy Yard, N-3 returned to the Submarine School at New London for patrol and training duty through 1920.