WW1 Submarines: From U-9 to the Frontkrieg Unit Guide

WW1 submarines went from an engineer's curiosity to the weapon that nearly starved Britain out of the war: between 1914 and 1918, German U-boats sank close to 5,000 merchant ships totalling more than 12 million gross register tons. Unrestricted submarine warfare dragged the United States into the conflict in April 1917 — and the convoy system ultimately broke the U-boat offensive. This article covers the submarine campaign of 1914–1918 in brief, then breaks down the submarine unit in Frontkrieg, a free browser-based WW1 grand strategy game with no pay-to-win, where the sub is the cheapest way to hunt enemy battleships. It is written for military history fans and players who want to squeeze every drop of value out of their navy.

U-9: the morning the world started believing in submarines

In August 1914 Germany had just 28 operational U-boats — set against the largest surface fleet on the planet, Britain's Grand Fleet. Admirals on both sides saw the submarine as a coastal-defence gadget and little more.

The illusion lasted seven weeks. On 22 September 1914, U-9 under Kapitänleutnant Otto Weddigen sank three British armoured cruisers — HMS Aboukir, HMS Hogue and HMS Cressy — in the North Sea in roughly 90 minutes. 1,459 sailors died, more than the Royal Navy lost at Trafalgar. U-9 carried a crew of fewer than 30.

The lesson terrified every admiralty: a capital ship without an anti-submarine escort is just an expensive target. The great fleets retreated to their bases, and the centre of naval war moved underwater.

Unrestricted submarine warfare: a bet on starvation

A submarine's power is stealth, yet international prize rules demanded the opposite: surface, stop the merchantman, inspect the cargo and give the crew time to abandon ship. A surfaced boat lost every advantage and was vulnerable even to an armed steamer.

So Berlin escalated, declaring the waters around the British Isles a zone where ships would be sunk without warning:

• in February 1915 the first unrestricted campaign began;
• on 7 May 1915, U-20 torpedoed the liner RMS Lusitania: 1,198 dead, including 128 US citizens — the international outcry forced Germany to back down;
• on 1 February 1917 unrestricted warfare resumed: the naval staff planned to sink about 600,000 tons per month and starve Britain within six months;
• in April 1917 the Allies lost over 860,000 tons of shipping — the peak of the entire campaign, with Britain's grain reserves down to a few weeks.

The gamble nearly paid off — but the price was fatal: on 6 April 1917 the United States declared war on Germany. For how the wider collapse unfolded, see our article on how World War 1 ended.

Convoys and depth charges: how the U-boats were beaten

The answer came not from a wonder weapon but from organisation. From May 1917 the Admiralty introduced the convoy system: merchant ships sailed in escorted groups of several dozen. The ocean is vast — a convoy is no easier to find than a lone freighter, but now every attack meant a fight with destroyers.

Alongside it grew a whole anti-submarine arsenal:

• hydrophones that could hear a submerged boat;
• depth charges detonating at a preset depth;
• Q-ships — decoy vessels with hidden guns;
• minefields such as the Dover Barrage across the Channel.

Tonnage losses fell while U-boat losses climbed. Of roughly 370 U-boats that served, Germany lost 178, and about 5,000 submariners died — nearly one in two. Britain was never starved out, while the Allied blockade of Germany itself worked in full. The complete numbers are laid out in Wikipedia's U-boat campaign article.

The submarine in Frontkrieg: unit stats

In Frontkrieg the submarine is a specialised naval predator, built in a harbour and living by the same rules as the historical U-boats: it strikes at point-blank range and picks its victims by class. Here are its exact numbers:

• cost: 30,000 money, 250 iron, 120 oil and 100 coal;
• build time: 10 in-game hours; requires a level 1 harbor and a level 2 factory;
• durability: 120 HP — more than a light cruiser (100), a third of a battleship (250);
• attack: 40, but strictly against fleets — it cannot touch land units, aircraft or buildings at all;
• defence: 30 against naval targets;
• upkeep: 12 money, 2 oil and 2 coal per day.

The defining trait is engagement range. A cruiser bombards from range 60, a battleship from a commanding 100, while the submarine, a true raider, must close to melee. In exchange it costs 40% less than a battleship (30,000 vs 50,000 money) and builds 6 hours faster.

Submarine tactics: hunting battleships

Naval combat in Frontkrieg rests on a counter triangle: the submarine gets a ×1.6 bonus against battleships but a ×0.7 penalty against cruisers; the cruiser shreds submarines at ×1.6, and the battleship guns down cruisers. The full modifier table is in our guide to unit types and counters.

That triangle gives the underwater fleet three practical roles:

• Battleship killer. A wolfpack of 3–4 submarines costs about 100,000 money and reliably sinks a 50,000-money battleship — a trade that pays for itself from the second kill onward, since the enemy also loses 16 hours of production time.
• Insurance against invasion. A transport carrying up to 70 units is nearly defenceless: a pair of submarines off your own coast deters landings better than coastal garrisons. How amphibious assaults work is covered in the naval warfare guide.
• Economic pressure. The mere presence of submarines forces your rival to lay down 22,000-money escort cruisers and burn coal on patrols — classic attrition warfare, familiar to the Kaiser's admirals.

What to avoid: sending a lone boat against a cruiser patrol (the ×0.7 penalty turns it into a target) and ignoring the sky — bombers carry a ×1.3 bonus against submarines. Budget your fuel too: 2 oil per day per boat means a flotilla of ten drinks 20 oil daily, so check the economy and resources guide before you commit.

If you enjoy tracing how each arm of service evolved — from the Somme to in-game counters — read our history of WW1 tanks.

Frequently asked questions

How many ships did submarines sink in WW1?

German U-boats sank close to 5,000 Allied and neutral merchant ships — over 12 million gross register tons in total — plus dozens of warships. The peak came in April 1917, when more than 860,000 tons went down in a single month.

Why did Germany resume unrestricted submarine warfare in 1917?

The Allied blockade was strangling Germany, so the naval staff gambled on starving Britain first: the plan called for sinking 600,000 tons per month to empty British granaries within 5–6 months. The bet failed — instead, the United States entered the war on 6 April 1917.

How did convoys stop the U-boats?

From May 1917 merchant ships sailed in groups guarded by destroyers equipped with hydrophones and depth charges. Attacking a convoy meant fighting the escort, so tonnage losses fell sharply while U-boat losses rose — Germany lost 178 of its ~370 boats.

How do I defend against submarines in Frontkrieg?

Keep cruisers near your valuable ships: they enjoy a ×1.6 bonus against submarines and fire from range 60, while the sub has to close to point-blank. Bombers help too, with a ×1.3 bonus. The worst guardian is a lone battleship — that is exactly what submarines hunt.

Conclusion: the weaker side's weapon that almost won

The 1914–1918 submarine campaign is the twentieth century's starkest example of asymmetric war: 28 boats challenged the world's mightiest navy, and three years later more than 12 million sunken tons had pushed an empire to the edge of famine. Guns did not win the fight — convoys did; organisation beat heroism.

Frontkrieg reproduces that logic faithfully: a 30,000-money submarine will not win you a fleet action, but it sinks battleships, wrecks invasions and makes your enemy overpay for escorts. Think you could have held the Atlantic in 1917? Join a new match — one starts every day, the game is free with no pay-to-win, and it runs straight in your browser. All our latest guides live on the blog.