The RN alone can not defeat the German invasion, as was demonstrated
What if the Nazi invasion of Norway failed?The reason the invasion failed could be the Royal Navy managing to stop the some or most of the invasion force and stop reinforcement and/or resupply of any German soldiers that land or the Norwegian government manages to properly prepare and with help from the British Army and Royal Navy the German invasion force is defeated.
The RN alone can not defeat the German invasion, as was demonstrated historically; the difference being the German air superiority over southern Norway, which is - to be blunt - the only part of Norway that matters strategically, in terms of population, transportation/communications/and in terms of proximity to Germany.
The campaign was lost, essentially, when the Germans seized Oslo, and the success or failure or that effort is entirely on the Germans and Norwegians; a more effective Norwegian mobilization will, of course, make a difference there.
Having said that, the problem for the Norwegians is that anything they realistically can do (absent the equivalent of the US intelligence advantage at Midway, for example) is still vulnerable to the Germans being able to
concentrate their invasion forces, rather than dispersing them along almost the entire Norwegian coastline. The Norwegians, of course, can't do that ... the Germans have the initiative, the Norwegians are reactive, so the relative advantage (even setting aside the reality the Germans have been mobilized since 1939) the difference in KM seapower vs. the RNoN, the difference in LW airpower vs. Norwegian airpower, even the difference between the available German army forces (~90,000+) vs. the likely Norwegian garrison around Oslo is a huge differential.
Especially given that sunrise in southern Norway in April is usually before 0700 and sunset not until 2000, which probably gives another hour of useful twilight ... 15-16 hours of daylight is an advantage to the side with the airpower advantage, for both offensive operations, air defense, transport, and simple reconnaissance.
And (IIRC) it is worth noting that the Allies (the specialized FAA dive-bomber units flying the Skua, in fact) managed to sink one German warship during the campaign, the light cruiser
Koenigsberg; the LW managed to sink three Allied warships, the light cruiser
Curlew and the destroyers
Bison and
Afridi.
If the British, French, and Norwegians conclude an alliance with a clear chain of command, joint staff, and British and French logistics and supply for the Norwegians
before the German invasion, that's one thing; but throwing together a coalition in wartime in the middle of an active campaign is pretty much a recipe for failure, as witness Norway, Greece, ABDA, and similar experiences. Worked for the Axis as well, of course; this sort of ability can't simply be made up...
Coalition warfare - and joint and combined operations involving the same coalition - is not something that can be extemporized.
The Allied were able to carry off combined and joint operations sucessfully in 1942-45 (and, for that matter, pretty much ever since) because of a tremendous amount of work, including a mature alliance system; that does not exist in 1940.
Best,