In April 1918, Bourke volunteered his Motor Launch to participate in the blockading of the Belgian harbour of Zeebrugge-Ostend, during the First Ostend Raid. The Motor Launches were detailed to rescue personnel from ships sunk in the blockade effort. Initially rejected from participating due to his eyesight, Bourke continued to volunteer his launch, despite knowing that volunteering put him and his crew in great peril. During action on the night of 23 April, Bourke's Launch picked up 38 sailors from the blockship and towed the crippled "ML 532" out of the harbour. For showing "the greatest coolness and skill in handling his motor-launch", Bourke was awarded the Distinguished Service Order (DSO).