I think in the West we tend to see events through a US perspective and that the attack on Pearl Harbor was the first indication of Japanese ill-intent. Just based on memory from readings long ago, the Japanese had made very clear their expansionist philosophy throughout the late 1930's and almost started a war directly with the UK over its funding of the Chinese Nationalist government.
Not really the first indication is probably the invasion of China but specifically though both the UK and US had alerted forces, the British were manning beach defences and the US had dispose its air force to prevent sabotage. hmm.
The UK and US both had and shared intel on Japanese naval mobilization so they knew something was happening not when or where. There is a specific sequence of events leading to the Japanese attack on the western powers.
At the time of the Japanese decision Germany has occupied all western Europe the USSR looks like its going to collapse and there is a good chance the Suez Canal will be captured.
At the same time FDR has declared an oil embargo which will only be lifted if Japan leaves the FEIC and China. The IJN has informed everyone that with the embargo they have fuel oil for the Navy for 3-6 months operations after which the USN will be able to sail into Tokyo Bay and flatten Cities one by one.
This persuades the IJA to release divisions for the attack on the DEI.
TTL Britain and France and the Dutch are in a war, but it not a major naval war, the Red Army is intact the US not being aggressive.
Maritime patrol aircraft? You mean those planes the RAF is hoarding to bomb German industry next year?
Well their orders as at April 13 are to prioritise German Troop concentrations, Transport and the Ruhr Oil industry. So no they would be bombing Troop concentrations, Transport and the Ruhr oil industry with a passing look at burning a few German cities just to remind folk that everyone can do it.
Slightly later most of the MR assets were based in South and West England to cover inbound convoys and presumably TTL Norway Bound and cross channel as well. To do that as at 1 November they had
22 GR & Fighter Sqdns, total IE 402, total IR 14, actual strength 464, average availability 187.
7 Flying Boat Sqdns, total IE 36, total IR 15, actual strength 58, average availability 14.
1%BD FAA Sqdns (812, %BD 700), total IE 12, actual strength 12, average availability 9
The fighter squadrons being Blenheims maybe some PRU flights with Spits. Lot of ocean to cover with 200 a/c
