A comparison between the Attack on Colombo IOTL, and a possible Attack on Singapore ITTL.
Colombo in what was at the time Ceylon, was a historic port city, with a long history. Singapore however was a product of British Imperialism, and prior to 1819, hadn’t as we understand it existed. By the time of TTL, while Colombo had slipped into a gentile colonial existence, Singapore had for strategic reasons become the centre of British defence plans in the Far East. The British government had spent despite the Great Depression, the sum of £60 million, equivalent to 2.5 billion pounds in today’s money, on the building of a protected naval base. The Japanese attack against Ceylon in 1942 after the fall of Singapore, was against a poorly prepared and equipped base, that hadn’t been prepared for war, during the inter-war years. And British forces that had suffered a series of catastrophic defeats in the preceding months, with the subsequent lowering of morale. While at the same time the British were under pressure in North Africa, which meant that they didn’t have resources to spare. And thus given that they were also still fighting battles against the Japanese in Burma, Britain was stretched very thin. In addition, unlike Singapore, which is at the end of an ever constricting area, Ceylon is an island with basically empty seas on three sides.
Singapore however is a small island, that is at the bottom of constricted area, with outlying islands to the East, tight waters to the East, West and South, and a major land mass to the north. It has a previously stated been substantially improved by the building of the Naval Base, at great cost. And due to recent events, both before and after the Japanese invasion of Malaya, there have been a significant number of improvements. Singapore while falling far short of the required numbers of planes, ships, guns, vehicles and men, required to make it the impregnable fortress it was claimed to be. Is however thanks to the minor improvements made prior to Japanese invasion of Malaya, and the lessons learned since, is now not the soft target it was IOTL. The combination of improvements prior and since the Japanese invasion, along with the experience gained from the attacks that have already taken place. Mean that Singapore is now a very tough nut, which will extract a very high price on any attempt by the Japanese main fleet, should it attempt to attack.
For the Japanese fleet it faces a number of challenges, in attacking Singapore that it didn’t when it launched its attack against Ceylon. Unlike Ceylon which a large island that other than to the West is basically surrounded by empty ocean, Singapore is a small island surrounded on all sides by land or very restricted waters. Any approaching Japanese Fleet, has to pass through very constricted waters, with numerous islands, reefs and extensive shallows. Under extensive air reconnaissance and any number of above sea and subsurface reconnaissance assists. The distance from Japan to Singapore from the Japanese home islands, is far greater than that from Singapore to Ceylon, with the possibility of resupplying at Penang. The Japanese Navy didn’t at the time or later, have a fleet train capable of conducting resupply missions at sea, so had to use either a sheltered area or harbour, in which to resupply especially oil. And given the distance between the Japanese homeland and Singapore, the Japanese Fleet will require at least one oil resupply, on either the outbound or return trip.
Any such attack will also face the problem that will face numerous attacks from British, Dutch and possibly some American forces, during their run towards Singapore. Before they can get into range of Singapore to launch their attacks, which will face significant opposition by the RAF forces based in Malaya and Singapore. Plus once they have carried out their attacks, they will have to withdraw, along predictably routes, when they will come under even more attacks. They also have the problem that if they use the whole of the Kido Butai, they are leaving both the Home Islands and the Japanese Pacific Territories open to attack by America forces. And that any attack is going to face a prepared defence, that for all the minimal success that the Japanese have enjoyed to date, is only getting stronger day by day. The Japanese as they did at Pearl Harbour, can only launch two or maybe three attacks, before they will have run out of munitions, and have to retire. Any attack at this time is going to see the Japanese take significant losses, while the British who will have moved their major naval units away to a place of safety. Will rapidly recover and replace any aviation losses, and repair such material damage that the Japanese inflict. Remember those big coastal guns that the British emplaced around Singapore, this is what they were designed for, and any Japanese ships that get into their range is going to be sunk. An attack by the Japanese Fleet, at this time, is going to be a major mistake.