During World War II, when Japanese planes were conducting airstrikes on Calcutta every other day, the British Indian govt had to put up a robust defense system all across the city. The Japanese planes, in those days, had to dive to a certain level to bomb. So helium-filled balloons were placed on top of all important buildings of the city and Howrah Bridge. A slight contact with the balloons would make them burst, causing the plane to crash.
Victoria Memorial was painted black, and grasses were planted on the Tala tank to make it look like an open green field from above.
Sirens were put at important junctions; street lights were covered, people were asked to cover the upper portion of their car's headlight, and even household bulbs were asked to keep dim with a cover after dusk. Citizens were asked to stay inside their houses, closing the doors and windows at night.
The night sky of the city turned into a battleground over the next few days, as the skilled pilots of the British Air Force and the allied countries started attacking and destroying several Japanese fighter aircraft, toning down the aggression.
The Kidderpore Dock got worst hit by the bombings in 1943. Japanese fighter planes attacked in the morning that day, stunning the British intelligence unit. As many as 43 people were killed. A bomb missed the target Central Telegraph Office at Dalhousie and fell on the entrance of Mangoe lane. A second bomb fell at the intersection of Writer's building and American Flying Club. A part of St. John's Church got damaged when a third bomb fell on its lawn. A bomb fell at Hatibagan market too, which didn't explode.