The small boat whipped up spray as it swerved to avoid the pursuing US coastguard vessel.

Crashing over the choppy waters of the San Diego bay, it raced up the harbour, weaving and feinting, columns of smoke bursting upwards on its starboard side when a concussion grenade was hurled on board.

The ending, when it came, was sudden.

After roughly 10 minutes of back and forth chasing, the coastguard boat finally drew level with its target and an officer, crouching out of his seat, fired a single, non-lethal shot to incapacitate the “pilot” of the rogue vessel.

The pursuit was a drill training San Diego authorities to intercept migrants who cross into the US from Mexico via the Pacific Ocean.