The gun was first fired on the morning of 13 February 1941, when the equipment was towed to a stretch of track near Kingston for calibration tests. Several rounds were fired out into mid-channel; the results were sighted and marked by observation posts on the cliffs at Dover.
On February 13, 1941, the gun was initially shot when moved to a section of track near Kingston for testing. Rounds were discharged into mid-channel; these were observed and recorded at observation posts on Dover cliffs.