The Dawn of the Submarine: U-21 sinks HMS Pathfinder

In 1914 submarines were still a novel idea. Many nations had not utilized them until 1900, Germany not until 1906. Soon their worth would be proven for the world to see. WWI was beginning, and with it came the first submarine-launched torpedo kill in history, changing the face of naval warfare forever.

SM U-21 was commissioned in October 1913, a type U-19 class submarine in the Imperial German Navy. She was posted to the Heligoland Naval Base under the command of Kapitan Leutnant Otto Hersing. This small submarine with a crew of 29, one of only four in its class, was going to make history within the next year.

On August 1, 1914, Germany declared war on Russia, and the crew of U-21 and her sister ships were called to their vessels, to prepare for war. Almost immediately U-21 moved out to the Dover Straits, to search for British ships. Hersing’s first two attempts were unsuccessful, but his third patrol proved more fruitful.

HMS Pathfinder, a scout cruiser based at Rosyth Naval Yard in the Firth of Forth, was patrolling the Firth with 8th Destroyer Flotilla. There had been reports of a U-Boat in the area, and Pathfinder was tasked with protecting the important merchant shipping and military vessels which frequented Rosyth docks.

German U-Boats in Kiel. in 1914. SM U-21 is in the far right in the front row.
German U-Boats in Kiel in 1914. SM U-21 is on the far right in the front row

On September 5, 1914, SM U-21 was sitting on the surface, charging her batteries using diesel generators. Suddenly, her crew spotted a smokestack on the horizon. They immediately dove, sitting just below the surface with their periscope above, preparing to attack. However, the cruiser changed course, reversing her direction in a zigzag patrol. The line of destroyers behind her turned towards Rosyth; their patrol finished for the day.

U-21 could not keep up with its prey, as the cruiser had a speed of 25 knots, to the sub’s 9.5 while submerged. Hersing decided to sit patiently, again on the surface, charging the batteries, ready for the cruiser to return later in the day.

His ship and his crew had to be completely ready for when an attack commenced. Every man and machine on board needed to operate in harmony with one another. For the time being, the crew could relax slightly, although the tension of impending combat hung in the air around the untested crew.

HMS Patrol, a sister ship to HMS Pathfinder
HMS Patrol, a sister ship to HMS Pathfinder


The men of U-21 were in the midst of a new age of naval warfare, and fittingly in a contest between the old and the new. 

Pathfinder was a relatively modern ship, but was based on the old idea of a powerful and seemingly invincible surface fleet. These substantial, steam-powered vessels patrolled the seas protecting vital shipping lanes. 

They had large crews. Pathfinder had almost ten times that of U-21, despite being around twice her size. They sat on top of the water, for the world to see. Stealth was not considered in their design, but rather speed and armament. 

The U-boats had a different approach. Early submarines were slow, cramped, and lightly armed, with only six torpedoes and a deck gun. U-21, however, was about to show the world that these strange new weapons of war were a force to be reckoned with.

In the mid-afternoon, around 1500, U-21 spotted her prey again. The cruiser’s stacks appeared over the horizon, and Hersing commanded his sub to dive. He moved into an attack position. At 1543 he gave the command, a single G Type torpedo slid out of the forward tubes of U-21. It sped towards its target, around 2,000 yards away.

An early German torpedo, the C-45-91, U-21 would have carried these for less important targets, as the G series was very expensive, and only for use on high value targets. Image Source: Wikipedia Commons By Nick-D - Own work, CC BY-SA 3.0,
An early German torpedo, the C-45-91. By Nick-D – CC BY-SA 3.0

On board Pathfinder, the crew did not suspect anything until it was too late. Suddenly a lookout cried “Torpedo!”

The captain took immediate evasive action, throwing the wheel hard to port while reversing the starboard engine, trying to turn the ship away from the certain death which sped towards them. The cruiser did not have enough speed to execute her maneuver in time. Shortly after it was spotted, the torpedo struck her just below the bridge, exactly where Kapitan-Leutnant Hersing had hoped.

Pathfinder shook with the explosion and lurched leeward. Almost immediately after the torpedo hit, another explosion rocked the ship, this time from the forward magazine. Cordite bags, used as a propellant in the ship’s artillery, had caught fire and caused a chain reaction. The cordite and artillery shells had exploded, destroying the forward half of the ship, and sending the bow plunging into the sea at an angle of almost 45 degrees.

The sinking of HMS Pathfinder, the ship was racked by explosions before finally succumbing to the deep.
The sinking of HMS Pathfinder, the ship was wracked by explosions before finally succumbing to the deep

The crew scrambled to get off, but to no avail for most. There was no time to lower her lifeboats. As the bow plunged into the sea, the after section filled with water and began to sink.

Men jumped overboard, while others screamed in agony from burns and injury. The sea was awash with bodies, debris, soot, and blood. 2,000 yards away, a periscope sat bobbing, then slowly moved away.

The cramped interior of U-1. While U-21 was slightly larger, it certainly wasn't much more spacious. Ships always have space as a precious resource, and that goes double for Submarines. But despite their small size and uncomfortable interior, they would become a terror. Image Source: Wikipedia Commons By de:User:Schoringer - Transferred from de.wikipedia to Commons., CC BY-SA 3.0,
The cramped interior of U-1. While U-21 was slightly larger, it was not more spacious. By Schoringer – CC BY-SA 3.0

The sinking of the Pathfinder proved once and for all that submarines were a viable weapon of war. The British Admiralty at first did not believe that a surface ship of her size could be sunk by a submarine-launched torpedo, attributing her destruction to mines.

However, eye witness accounts, from both British and German crews confirmed U-21 did indeed sink the Pathfinder.  It was the first submarine launched torpedo kill in history. Of her likely 268 man complement that day, only 18 are known to have survived; a new age of naval warfare had begun.

Gabe Christy

Gabe Christy is one of the authors writing for WAR HISTORY ONLINE