Figure 1.--Here we see Calcutta children sheltering in a slit trench during a Jaopanese air raid. The photograoph is dated June 30, 1944. The caption read, "Fearful Eyes of the Innocent: Fear grips the fces of these Bengal children as they sit vin a slit trenches and anxiously watched strafng Jap Sers pass overhead. Chikdren like these the world over have never kniwn the wimders of peace being born into a maddened civilization brought on by the tyranny if the Axis. Bamboo poles and basketwork support the sudes of the trench offering the native youngsters protection."

The Japanese from bases in Indo-China (Vietnam) and Thailand after Pearl Harbor swept through Southeast Asia seizing Malaya, Singapore, and Burma only stopped bt the monsoon rains (May 1942). The British, commonwealth and Chinese forces made a stand in eastern India on the Burmese frontier. There strengthened by the flow of supplies through Calcutta they were able to block further Japanese advances. And from bases in eastern India supplies to China were flown over The Hump. The Japanese wanted to continue their offensive into India. And naval dominnce would have cut off the Allied forces in India from reinforcement and supply. Reverses in the Pacific War, however, meant that the Imperial Japanese Navy was unable to control the Indian Ocean. This meant that the only way to cut off supplies was aerial bombing. And as most of the supplies arrived at Calcutta, that Indian city and port became the primary target of the Japanese bombers. The Japanese began bombing raids (late-1942). They continued eposoduically through 1944. While they caused some damage in Calcutta, the campaign proved to be a mere pin-prick in the massive Allied supply effort. THe inaccuracy of World War II bombers and the small loads of the Jopsnense bombers mean that they did not hve the capacity to severely damage the Calcutta port infrastructure. A large raid would be about 30 bombers. At the time, the Allies were routinely staging thousand bomber raids in Europe. With reverses in Burma and the Pacific, and no longer able to supply air bases in Indochina and the Andaman Islands, the Japanese ended the campaign (December 1944).

Strategic Situation

The Monsoon rains after the Jaopanese seized Burma stopped the Japanese from continuing on into India (May 1942). The Japanese did, however, begin to bomb eastern India. The main target was Calcutta, the primary port in eastern India. Much of the supplies for the the Allied forces which regrouped along the Indian-Burmese laned at Calcutta and then transported by train to the Allied camps. The Japanese hoped to cut off these shipments by control of the Indian Ocean. A Japanese carrier task force wreaked havoc in the Indian Ocean (April 1942). Further such actions, however, had to be cancelled after heart was cut out of the First Air Fleet Midway (June 1942). This left the Japanese fully committed with the Americans in the Pacific. This had two consequences. First, the Allies were able to supply gotces in eactern India. Second, the Japanese could not supply their forces by sea using the port of Rangoon. This severely limited the supplies that were delivered to the forces in Burma. Thus while Calcutta becme an important target, the Japanese were limited in the supplies tht could be delivered for a major air campaign. And the Thai-Burma Railway did not solve the supply limitations.

Calcutta/Kolkata

The major port in eastern India was Calcutta, modern Kolkata. It is through the port of Calcutta that the suplies for the Allied forces flowed. They were then transported by rail. The supplies landed in Calcutta were not only the Allied front line forces facing the Japanese along the Burmese border, but also the aid being delivered to China by air over The Hump. With the loss of Burma, supplies to China could not be delivered over the Burma Road. The supplied delivered to China were primarily for American air operations in China abd to build a Chinese Air Force. Budge Budge was part of the port and the location of storage tanks. Being close to Kolkata and on the shores of Hooghly River river made it a strategic location for oil storage. The Allies built a pipeline friom Budge Budge to its militry forces on the Burmese frointier anbd eventully all the way to China along the Ledo Rioad as the Allies cleared the Japanese friom northen Burma (1945). Without Calcutta, the Allies would have been unble to aid China. The CBI Theater had the lowest priority of all the Allied commands. Even so it was massivly larger than the supplies available to the Japanese. Calcutta was not the only target, Chittagong to the east waa also hit, in part to create a diversion to complicate air defense. The principal target from the beginning was Calcutta because this was the major port and where most of the supplies wer being delivered. One source reports, "Calcutta was just within range of Japanese bombers, and through-out 1942 and '43 they did their best to disrupt the operations of the port and create panic among the population."

Japanese Supply Lines

In World War II the principal way of delivering supplies exceot for the Germans and Soviets in the Eastern front was by ship. This created a significant problem for the Japanese after MidWay (June 1942) when they began to lose naval dominance and the after reciving torpedoes that worked, the American submarine camaign befan to kick in (1943). The Japanese seized Rangoon a major port cuty (March 1942). The British destroyed the port facilities before withdrawing. And by the time the port was repaired, the naval war had changed dramatically with the stunning American victory at Midway (June 1942) and the increasing effective American submarine campign. This meant that the Japanese soon had difficulties getting supply ships to the port. This is why they made such a detemined effort to build the Thai-Burma Railway. But even when constructed this did not solve the supply problem. It was a narrow-gage railway and the Japanese pressed by the Americans in the Pacific and bogged down in China, did not have the planes and supplies to mount a major bombing campaign. The Japanese also used bases iun the Andaman Islands, but after as the War progressed the Japanese had increasing problems supplying the islands.

Japanese Aircraft

The Japanese did not have any four-engine long range bombers like the American B-17 and B-24 and the British Lancaster. They were experminentuing with two four-engine bombers at the end iof the War. The did have a small number of a long-range flying boat which could carry bombs -- the Kawanishi H8K (Emily). What the Japanese used for long-range missions was two two-engine bombers. The long range, achieved primarily by the lack or limited armor and armament and by relatively small bomb loads which of course limited their potential combat impact. The Japanese used the Mitsubishi Ki-21 (Sally) for raids on Calcutta. It had a range of 1,680 miles and a 2,200 lb bombload. The Sallys were extensiuvely used to bomb Chinese cities, but sfter the arrival of the Anmeruican AVG Flying Tigers experuebced heavy combat losses. Calcutta was just within the Sally's range from airfields in northern Indochina (Vietnam). Adaman Islands bases were also used, but the Japanese had troubkle supplying the Adamans. The Mitsubishi G4M (Betty) was a Navy bomber with a slightly more limited range and a somewhat smaller bomb load. The Betty was the bomber primarily encountered by Americcsnbs in the Pacific. The Japanese built only a fraction of the number of bombers the Allies built, about 2,100 Ki-21 Sallys and 2,400 G4M Bettys. This explain the small number of these bombers used in the Calcutta raids. Compare this with the heabilly armored bnd armed American B-17 with a range of 2,000 miled (actually 2,700 miles with a bomb load like the Japanese bombers carried). The B-17 carried 4,500 lb of bombs, but could carry 8,000 lb or shorter runs. On the few daylight runs, the Japanese used the Nakajima Ki-43 and Mitsubishi A6M Zero fighters as escorts. .

Campaign

The reverals experience by the Imperial Navy in the Pacific meant thst the Allies would retain control of the Indian Ocean and could not stop supplies from reching the Allies by sea through the port of Calcutta. Their only alterntuve was to close Calcutta by aerial bombing. The Japanese bommbing campaign was conducted (late-1942-44). As best we can tell it was a low-level operation. The initial air raids were night raids with a smaller number of bombers. One of the larger raids, howver, involved less than 30 bombers. Given the inacurascy of World War II bombing, this was not going to hve a major impact. In Europe the Allies were conducting thousand bomber strikes. The targets in Calcutta was the Kidderpore docks, Dum-Dum Airfield, and the Howrah Bridge. over the Hooghly River. Majerhat Railways Station was a key rail hub for the supplies flowing toward the Allied fighting forces on the Burma frontier and China. The first substantial raid was a daylight attack (December 20, 1942). Some 500 people were killed, many coolies (porters) at the docks. Ships were damaged. And several smaller raids followed the next few days (December 21-24). The Japanese expanded bombing operations in the new year, beginning with a raid Janury 15, 1943. Bombing ar night, many of the bombs fell in open fields ('maiden'). [Mukherjee] The most devestating raid was launched from the Andaman Islands in daylight (December 5, 1943). The bombing frightened the city residents and damage was done to the docks and warehouses. Some 335 – 500 people were killed, agsin primsrily coolies and others working at the docks. Maximum of the victims of this raid were coolies and laborers sleeping in their quarters. A few vessels were damaged in the harbor. The last raid was conucted (December 24, 1944). After this the deteriorating military situation foirced the Japanese to end the raids on India. The Allied supply effort was so masssive that the Japanese air raids proved to be mere pinpricks. The Japanese bombing did not seriously impair the flow of supplies to the Allied forces. Japan simply did not have the bombing forces to do this or the ability to supply a major air effort even from Indochina bases.

Air Defene System

Calcutta had a substantial air defense system. There were squadrons of Hurricanes, Spitfires, Typhoons, Lysanders, and Beaufighters at air bases around the city. The British built a substantial airfield large airstrip at Baigachi (near Dankuni). They also used the existing infrastructure at Dumdum Airport which became one of the busiest in the world. At first there was no radar facilities, but radars were eventually added to the air defense system. There was also a Balloon Squadron. An Indian blogger writes, "Red Road (Maidan) in Calcutta (Kolkata) was transformed into landing strips overnight. Some historians point out this activity to more of a morale booster to the local population rather than practical usage. All the open fields around the Maidan area were converted into open warehouses housing jeeps, oil tankers, and other engineering divisions. Apart from this Salbani Airfield, Madhaiganj Airfield and Chakulia Airfield were also used." [Mukherjee] As a result the raids were mostly high alditude night time raids. This prevented any accurate targetting. The British dispatched night fighters (1943). Air defense was complicated by the Fact that the Japanese did not mount a sustained bomning campaign. Tying up large numbers of modern fighter aircraft for the occasional Japanese raids did not make military sence. There were many other priorities. Calcutta did not have bomb shelters. Rather slit trench were dug where people near the docks and other priority targets could shelter. The shelter here is a good example (figure 1).

Sources

Mukherjee, Subhadip. "Japanese Air Raids on Kolkata during WWII," Indian Vagabond Website (September 4, 2017).

Created: 5:11 PM 1/22/2019
Last updated: 7:52 AM 1/23/2019