Note - OTL the 3 April raid by 10th Air Force was against the docks in Rangoon. Major Lewellyn as killed OTL on an attempted raid against Rangoon by two B-17s on 2 April (his plane crashed). For this ATL all bombers went against Port Blair on 2 April instead of a split raid and then the 3 April raid was also against Port Blair.
3 April 1942, Port Blair Andaman Islands - At 0600 on the morning of 3 April, the US 10th Air Force paid its second visit to the Japanese base at Port Blair, this time with six B-17E Flying Fortresses under the command of Brereton's aide Major Norman Lewellyn. However, this time the Japanese had a surprise in store for them. First, the unit commander at Port Blair made sure the five H6Ks flying that day were airborne by 0500 while the other six planes were dispersed in the harbor. Second, a shotai of Zeroes from the 22nd Air Flotilla were on patrol at 10,000 feet waiting to ambush any incoming raids. The big American bombers followed a similar plan as the day before with two concentrating on ships in the harbor, two attacking the seaplane base, and two bombing the docks and wharves. The Zeroes jumped the lead pair as they made their attack run against two large merchant ships and in the ensuing fight the B-17 piloted by Major Lewellyn was shot down while the other was heavily damaged. One Zero was shot down in exchange. Because the remaining H6Ks were dispersed in the harbor, the bombing against them was ineffective and strafing only managed to destroy one seaplane while the bombers attacking the docks managed to set several buildings on fire but no significant damage was done. With two fighters still harassing them, the bombers did not line up for an additional strafing run of the harbor and instead turned for home with the Zeroes chasing them out to sea. Brereton was deeply saddened by the loss of Major Lewellyn who had served with him for two years.
The morning of 3 April found Somerville's task forces in the Bay of Bengal approximately halfway between Trincomalee and Madras. With Boyd's carriers furthest out to sea of the three task forces, the ships turned northeast to head to their maneuver area 250 miles south of Visakhapatnam. At the same time, Force D was in its operations sending out radio signals mimicking a carrier group conducting flight operations. For those onboard the British ships and at British land bases, it was now a matter of waiting for the enemy to show up.
Nagumo's carriers were 800 miles south of Port Blair at 0900 and heading northwest toward Colombo on 3 April while Ozawa's ships transited the 10 Degree Channel and entered the Bay of Bengal. Onboard the Japanese ships, men played the same waiting game as their British counterparts. The day's reconnaissance reports were disappointing. Patrolling H6Ks reported nothing but merchant traffic at Visakhapatnam, Madras, Koggala, and Trincomalee although the crew of the Mavis flying over Madras had an exciting morning as they were chased away by two Blenheim bombers from No. 11 Squadron. Unfortunately for the Japanese, the H6K sent to investigate Colombo met the same fate as his counterparts from two days ago, this time at the hands of two Fulmars from No. 273 Squadron who were expertly vectored onto the radar contact by the inexperienced but fast learning crew manning Colombo's small radar station. There was a sense of unease onboard Nagumo's flagship about the lack of up to date intelligence on Colombo since the last successful mission over the port was 48 hours earlier. Nagumo and his staff waited for the expected report from I-7's floatplane, not knowing that I-7 had been sunk.