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do without, would also be affected by heavy rainfall. Incendiary bombing, which would become a favourite strategy with the Allies against Japanese targets elsewhere as the war progressed, would naturally be less effective during the middle part of the year in Hong Kong. Heavy rainfall also affects the performance of propeller aircraft by cooling their engines excessively.1 Overall, air operations of all kinds would be less effective or even grounded during periods of heavy rainfall.
The flip side of air operations is anti-aircraft defence. A simple, inexpensive device employed as an anti-aircraft measure was the barrage balloon. This was a large hydrogen-filled, dirigible-shaped balloon attached to a steel cable anchored to the ground or a ship and floated several hundred to several thousand feet above it. The cable was stronger than it looked, and was meant to discourage low-level air attacks by having the ability to damage or clip the wings of a low-flying aircraft. This forces the aircraft to fly higher, which decreases its attack accuracy, and aids the effectiveness of one's own anti-aircraft artillery and intercepting aircraft.16
However, a hydrogen-filled barrage balloon (in the days before helium use was common) is highly flammable. This is a liability during a thunderstorm, during which a spark of lightning could turn a barrage balloon into an incendiary hazard that is more dangerous to its user than to the enemy.
Cloud and fog.
Cloud and fog often went hand-in-hand with heavy rainfall to restrict air operations. Reconnaissance of Japanese positions would be very difficult. High level bombing or close support, favoured by the Allies and employed extensively in other theatres, would have to be cut back or even cancelled. If cloud and fog were present at the beginning of the amphibious stage of the Allied assault on Hong Kong, when the Allies would be at their most vulnerable, crucial air support would be inadequate or even lacking. If the Japanese contested the landing, and this was expected, the Allies would be faced with a precarious and probably dangerous situation.
While cloud and fog are most prevalent during the beginning of