Because of inadequate early warning systems (the first British radar stations became operational only towards the end of February), Japanese air raids were able to destroy 30 Hurricanes on the ground in Sumatra, most of them in one raid on 7 February. After Japanese landings in Singapore, on 10 February, the remnants of 232 and 488 Squadrons were withdrawn to Palembang. Japanese paratroopers began the invasion of Sumatra on 13 February. Hurricanes destroyed six Japanese transport ships on 14 February but lost seven aircraft in the process. On 18 February, the remaining Allied aircraft and aircrews moved to Java, with only 18 serviceable Hurricanes out of the original 99. That month, 12 Hurricane Mk IIB Trops were supplied to the Dutch forces on Java. With dust filters removed and fuel and ammo load in wings halved, these were able to stay in a turn with the Oscars they fought. After Java was invaded, some of the New Zealand pilots were evacuated by sea to Australia.