The United States Navy focused on countering enemy U-boats in the Atlantic Ocean and the Mediterranean Sea while convoying men and supplies to France and Italy.

Because of United States's late entry into the war, her capital ships never engaged the German fleet and few decisive submarine actions occurred.

In order to relieve the British and European allies already on the battle front, the United States Navy was tasked with transporting millions of U.S. soldiers and supplies across the Atlantic to France.

Congress declared war on April 6, 1917, which meant the United States Coast Guard automatically became a part of the Department of the Navy.

[Note 1] Destroyers and similar escort warships were considered the most effective means of sinking enemy submarines and protecting merchantmen.

Gunner's Mate First Class Osmond Ingram noticed the torpedo just before it struck and alarmed the K-gun crew, who began firing depth charges.

The first combat loss was USS Jacob Jones, a destroyer, which was sailing to Ireland in a zig-zag pattern with five other warships from Brest.

Commander David W. Bagley ordered his crew to abandon ship, and as she sank the armed depth charges aboard began to detonate, adding to the already heavy casualties.

During the action, a few depth charges became loose aboard Christabel, and at great personal risk Ensign Daniel Augustus Joseph Sullivan secured them, earning him the Medal of Honor.

[12] The following day, USS San Diego suffered an explosion while sailing from the Portsmouth Naval Yard to New York City.

The armored cruiser was northeast of Fire Island when it was thought a torpedo struck her port side below the waterline at the engine room below.

On August 6, she was patrolling off North Carolina's Diamond Shoals when she encounter a sinking cargo ship, Merak, a victim of U-140.

According to the submarine war diary entry, the U-boat dived and maneuvered into an attack position, firing one torpedo out of the stern tube at 2015 from a range of about 550 meters (600 yd).

Minutes later, the torpedo hit Tampa and exploded portside amidships, throwing up a huge, luminous column of water.

Alerted by the convoy flagship, whose radio operator reported having felt the shock of an underwater explosion at about 2045, search and rescue efforts over the succeeding three days turned up only some wreckage, clearly identified as coming from Tampa, and a single unidentified body.

Rear Admiral Lewis Clinton-Baker, commanding the Royal Navy minelaying force at the time, described the barrage as the "biggest mine planting stunt in the world's history."

In the Mediterranean, Austro-Hungarian forces in northern Italy and the Ottoman Empire were two major threats, though by 1917 their navies were mostly defeated or blockaded by ships of the Otranto Barrage.

Heavy seas prevented an immediate assessment of possible damage to the submarine but later evaluations credited USS Lydonia and HMS Basilisk with sinking UB-70 when she failed to show up at any port.

[28] Twelve U.S. submarine chasers under Captain Charles P. Nelson were part of an attack on the Austro-Hungarian held naval base at Durazzo, Albania.

The battle began on October 11 with Italian and British aircraft bombarding Austro-Hungarian concentrations within the city while the allied fleet was still crossing the Adriatic Sea.

For his leadership and courage at Durazzo, Captain Nelson received the Navy Distinguished Service Medal as well as other foreign decorations.

[29][30] Coast Guard Captain Leroy Reinburg of USS Druid engaged enemy submarines near the Strait of Gibraltar in November 1918.

The Druid was operating as part of the Gibraltar Barrage, a squadron of U.S. and British ships assigned to keeping enemy U-boats from passing from the Mediterranean into the Atlantic.

HMS Privet reported that she shot a hole through one of the submarines' conning towers with a 4-inch (100 mm) gun but other than that no other damage was thought to have occurred.

USS Druid and her compatriots were successful in defending the strait and on the following day the Americans helped rescue the British crew of the battleship HMS Britannia which had been torpedoed by UB-50 while passing through Gibraltar into the Mediterranean.

In December 1914 the German auxiliary cruiser SMS Cormoran was commerce raiding in the South Pacific, when her commander put in for provisions on the then neutral island of Guam, a United States territory.

When the war with Germany finally began on April 6, 1917, the old schooner USS Supply was ordered to demand the Cormoran surrender or be sunk.

In an attempt to prevent this, the captain of the USS Supply ordered the United States Marines on board to open fire on German crew.