Lemp strains to identify the ship in front of him.

CHRISTIAN JENTZSCH: It's behaving, in his opinion,

like an auxiliary cruiser because it's zig-zagging

and it's blacked out.

And he even imagines to have seen gun platforms.

NARRATOR: In Lemp's mind, that is enough proof

this is some kind of armed enemy ship fair game

to be attacked without warning.

With torpedoes ready--

[non-english speech]

NARRATOR: --a little before 8:00 PM Lemp

fires the first to U-boat torpedoes of World War II.

A hydrophone operator monitors them by the sound

of their propellers.

One speeds towards the target.

But there is a problem with the second.

It should grow fainter but instead is getting louder.

Fearing that it will circle back and strike them,

Lemp orders the U-boat deeper.

It is a scenario they train for, even in peacetime.

The standard procedure is to dive below the depth

that a torpedo would pass.

NARRATOR: It could be tight.

U-30 is more than 210 feet long.

And as the bow angles down, the stern goes up.

They must get the whole U-boat out of danger.

They have no way to visually monitor the threat.

Their only source of information is what the hydrophone operator

can hear.

[propeller whirling]

When the noise finally fades away,

the torpedo no longer poses a threat.

Relieved, Lemp surfaces to investigate.

With darkness falling, he moves in for a closer look.

The first torpedo had struck the ship.

But as Lemp surveys the crippled vessel,

he realizes that something is wrong.

They check the silhouette of the large ship against the Lloyd's

Register of vessels.

When he saw the scene of action,

he realized that he was mistaken.

It wasn't an auxiliary cruiser.

It was a steamer with a lot of civilians in the water.

NARRATOR: An intercepted radio transmission

confirms his fears.

It identifies the ship as the passenger liner

SS Athenia bound for Canada.

Lemp has made a huge mistake.

His orders were clear.

Sink only warships, troop ships, and enemy merchant vessels.

Hitler and the German government

still hope for some kind of settlement

agreement with Britain.

And so they don't want to aggravate the British more

than necessary.

NARRATOR: Now, on the very first day of the war,

Lemp has sunk a passenger vessel without warning.

Comparisons are immediately made to the sinking of RMS Lusitania

by a U-boat in World War I, an act that helped end American

neutrality and brought the United States into the war

against imperial Germany--

the exact scenario Hitler hoped to avoid

with his strict instructions.

Now the sinking of Athenia sets off a new political firestorm.

Many of the 1,103 passengers aboard

are Canadians, Americans, or European refugees

escaping the war.

118 civilians are dead.

Hitler and his propaganda minister, Joseph Goebbels,

vehemently deny German responsibility for the attack.

The man responsible for Hitler's headache

is 26-year-old [inaudible] Fritz-Julius Lemp.

CHRISTIAN JENTZSCH: He was born as a son

of an army officer in China before the First World War.

He entered the [inaudible] Marina in 1931.

And he went to the new created submarine arm in 1936.

NARRATOR: He was assigned command of

his own Submarine U-30 in 1938.

Lemp recognizes the potential fallout from his error.

He makes no radio report of the sinking

and continues his patrol.

He has to keep it secret.

And he decides to stick exactly to the submarine protocol

for his future attacks.