In the city of Harlingen, over 400 German soldiers were left behind, ordered to defend the town against the advancing Canadian troops. On 15 April 1945, they began carrying out acts of destruction. The bridges in the Midlummerweg road over the Ried Canal, the Kimswerderweg road over the Bolswardervaart Canal, and the railway bridge over the Achlumervaart Canal were all blown up. 

The occupying forces sunk ships in the harbour mouth and in the Nieuwe Willemshaven harbour to hamper shipping from the Wadden Sea. The engines of the shipyard, cranes and floating sheerleg cranes were destroyed, although the shipyard and port installations themselves were spared. 

To delay the advance across the inland waterways, ships were also sunk in the Zuiderhaven (South Harbour) before the Kleine Sluis (Lesser Lock) and in the Noorderhaven (North Harbour) before the Grote Sluis (Great Lock). These locks were the only entrances from Friesland's hinterland across the water to the Wadden Sea. The present-day Van Harinxmakanaal and Tjerk Hiddes locks were only constructed after the war. Finally, several ships were also grounded at the Harbour Bridge and the Prince Hendrik Bridge. All in all, seventeen vessels had been sunk in Harlingen by the occupying forces. 

That the destruction could have been much greater is evident from the statement of the then Hafenkapitän Leutnant zur See (Harbour Captain Lieutenant at sea), Dr Hans Günter Heinze in 1983. He stated: 

‘Incidentally, as harbour captain of Harlingen, I was later able to ensure that the quay walls there were not blown up as planned, but that a few barges and a ship in the harbour entrance were sunk there as a lesser evil. 

The commander of the naval artillery there, as the local commander, also wanted to blow up the water tower and the locks in order, as he thought, to put the whole of Friesland under water. Only when I asked him whether he thought the Canadians would then stop their advance for fear of dying of thirst, and that if he had the bold plan to submerge the whole of Friesland through the small locks, he would have to leave the locks intact in order to close them at low tide, did the whole thing stop. To set the record straight, he only wanted to flood the area around Harlingen in defence of the city, but didn't know that the hinterland was a large polder covering Friesland.’  

During the Canadian artillery shelling of Harlingen on 16 April 1945, the harbour was also a prime target because German artillery was still positioned there. The tugboat ‘Edzo Jan’, with which the Hafenkapitän and some other German soldiers tried to escape, was discovered from the air during the liberation and hit by Canadian artillery shelling. This resulted in several deaths on board and the ship then returned to port.