Zeebrugge Mole Explained: Structure, Defences and the St George’s Day 1918 Assault

The Zeebrugge Mole, a huge crescent‑moon shaped concrete breakwater stretching 1.5 miles into the North Sea, was originally built in 1903 to shield Zeebrugge Harbour from violent western storms.

How the Zeebrugge Mole Was Built and Why It Mattered

By World War I, however, this immense structure had been transformed by German forces into a heavily fortified naval bastion guarding the entrance to the Bruges Canal. With its towering concrete walls, railway lines, gun batteries, searchlights and a lighthouse watch‑post, the Mole became one of the most formidable defensive positions on the Belgian coast — and the near‑impossible target of Captain Roger Keyes’ daring raid on St George’s Day 1918.

How German Forces Transformed the Mole Into a Naval Stronghold

In more detail, the aptly-named Mole is a crescent-shaped concrete breakwater viaduct, jutting in a north-easterly direction towards the North Sea. It was originally built to protect Zeebrugge Harbour from the harsh North Sea storms that swept in from the west.

Foreshortened View of the Mole after the Zeebrugge Raid

Concluding with a lighthouse at one end, the Mole is 1.5 miles in length and sturdily built. It was completed in 1903 to great ceremony by King Leopold III of Belgium. But little did anyone realise at the time, that the German forces would utilise it as a fort, heavily guarded by 1000 men and countless battery-guns. The lighthouse formed the ideal watch-post against allied invasions from the sea.

Entrance to the Bruges Canal

The causeway running along the Mole had been laid with a road and a railway within the shadow of a 15 foot concrete wall, 10 feet thick on the seaward side. This provided protection from the inclement weather (and during wartime) allied invasion. Incredibly, the top of the wall provided a secondary roadway and a further wall, 4 feet higher than the wall at its base.

Captain Roger Keyes and the Challenge of the 1918 Zeebrugge Raid

Any raiding vessel stood little chance of overcoming the strong ocean tides, harsh sea gales, countless gun emplacements, cannons, nets and artillery. And this without being spotted first by powerful searchlights or the lighthouse itself.

Captain Roger Keyes, chosen to raid the Zeebrugge Mole on St George’s Day 1918, must have been too aware of the challenges that he faced.