1. I didn't knew about Defence Regulation 18B, thanks for information.
2. Yes, I know. But they also hadn't marine divisions preprared for Operation Sealion. I just thought that they could reorganize four marine divisions into brigades.
3. It changed when British started to lose war.
4. Because they reformed Home Guards into units defending beaches and they think that Germans will launch another amphibious invasion.
5. This is first day of invasion and gas will be used.
6. Research over submarines was performed in secret.
7. I just thought that Soviet Union could develop their own submarine forces based on joint researches and create commerce fleet. This fleet could be used in fight against British Royal Navy.
8. Uboats are better that OTL. Engineers from Soviet Union and Germany found flaws in torpedoes and managed to repair them. I think that progress overtook OTL by 1-2 years.
Some ships of OTL Royal Navy were sunk by Unterseebootsflotilla - HMS Ark Royal, HMS Courageous, HMS Hermes during first days of the conflict. During Norwegian Invasion several others capital were sunk by Uboats - it was possible but didn't occurred in OTL because Uboats had flaws and torpedo attacks were badly performed.
1. Research before writing is the best tip that I can give anyone for any purpose.
2. Marine divisions are more than just a name and would require a lot of preparation, doctrinal advance and organization up to a decade before 1942. Is Germany preparing for an invasion of Britain in 1932?
3. It didn't change at any stage of either world war. This is an amateur error that is completely unnecessary.
4. A previous poster already supplied links showing the regular troops dedicated to defence of the area in 1940. By 1942, there will be a lot more troops available, the details of which can easily be researched. These would include the first and second line TA divisions, the reformed BEF, three or more Canadian divisions, the static County Divisions and numerous independent brigades, regiments and battalions. Have these all been sent home or disintegrated?
5. You are contemplating an invasion on a par with Overlord, which would take a bit longer than a day. Above and beyond that, there isn't a reason not to gas the Germans on the beaches and in their landing craft apart from artificially nerfing the British.
6. Submarine research in secret? It isn't possible to research and build a major submarine force in Europe without being noticed. This doesn't include mere observation, but shortages of materials in the German economy and the cancellation of other vessels to make way for submarines and destroyers. You don't seem to understand the complexities of naval construction; reading up some of the technical articles on NavWeaps will help you here.
7. The Soviet Union already built a large submarine force that was suited to their littoral purposes. There wasn't a large shipyard up in the Northern Fleet at this time, the Black Sea Fleet is stuck there and the Pacific Fleet
8. Why are they better? What happened to ameliorate the historical problems and issues and why did this occur? What did not occur due to this different concentration of effort? How were torpedoes tested? This violates the principle of performing operations on both sides of the equation.
How would a Norwegian campaign be possible without the large surface ships built in @ that couldn't be built if there was an earlier concentration on 'destroyers and submarines'?
Why is the Royal Navy not reacting to any of these quite considerable changes several years beforehand? It has a minimum of 12 capital ship/carrier size slips available, plus well over 100 capable of building destroyers/escorts; this doesn't factor in the smaller escorts.
The Royal Navy, when faced with the historical threat, had the following construction programme:
1928, 57m, 9 destroyers, 4 submarines, 4 sloops
1929, 56m, 1 6in cruiser, 5 destroyers, 3 submarines, 4 sloops
1930, 51.7m, 3 6in cruisers, 9 destroyers, 3 submarines, 4 sloops
1931, 51.6m, 3 6in cruisers, 9 destroyers, 3 submarines, 2 sloops, 2 minesweepers
1932, 50.5m, 3 6in cruisers, 9 destroyers, 3 submarines, 2 sloops, 2 minesweepers
1933, 53.6m 3 6in cruisers, 9 destroyers, 3 submarines, 2 sloops, 1 patrol vessel, 2 minesweepers
1934, 56.6m, 1 aircraft carrier, 4 6in cruisers, 9 destroyers, 3 submarines, 2 sloops, 2 patrol vessels, 2 minesweepers.
1935, 60m, 3 6in cruisers, 16 destroyers, 3 submarines, 1 sloops, 2 patrol vessel, 3 minesweepers
1936, 70m, 2 battleships, 2 aircraft carriers, 2 6in cruisers, 5 5.25in cruisers, 18 destroyers, 8 submarines, 2 sloops, 1 patrol vessel, 3 minesweepers
1937, 78.1m, 3 battleships, 2 aircraft carriers, 5 6in cruisers, 2 5.25in cruisers, 15 destroyers, 7 submarines, 3 sloops, 3 patrol vessels, 4 minesweepers.
1938, 93.7m, 2 battleships, 1 carrier, 4 6in cruisers, 3 5.25in cruisers, 3 fast minelayers, 3 submarines, 1 aircraft maintenance ship
1939 69.4m, 2 battleships, 1 carrier, 2 6in cruisers, 1 fast minelayer, 16 detroyers, 20 Hunts, 2 sloops, 56 corvettes, 20 minesweepers
Additionally, we have the following material from Hyperwar:
Naval strength required by 1942:
A.) Naval strength 1934
B.) 'D.R.C. standard' 1934–35 (Defence Requirements Sub Committee)
C.) 'Two-power standard' 1935–36
Capital ships
A.) 15
B.) 15
C.) 20
Aircraft carriers
A.) 5
B.) 8
C.) 15
Cruisers
A.) 50
B.) 70
C.)100
Flotillas of destroyers
A.) 9
B.) 16
C.) 22
Submarines
A.) 50
B.) 55
C.) 82
Escort vessels, minesweepers, etc.
A.) 51
B.) 120
C.) 226
The RN Naval Standards of 1934–36 (Hyperwar, British War Production Chapter II)
As said previously, stop before you get too far in, as the feedback will be negative and could prove to be discouraging. Read up on the source material and previous attempts before going over old territory.