Thats actually a good suggestion - once you have hindsight. In hindsight the westwall was a huge waste - akin to the Maginot line or almost.
But without any westwall, the possibility of a strong French offensive during the fall of 39 gains serious momentum, so alot of these materials would have to go to a stronger land army, in order to check that threat more credibly. If it all goes to the Navy, things could get ugly before the ships are ever put to use.
Yes as long as we remember that the West Wall was Hitlers plan and not the General Staff...most of the cost was due to Hitlers demand that it be completed in a few years when it should have been planned over a decade time....Hitlers demands have a lot to do with why German rearmament cost so much and achieved so little.
The German General Staff had already concluded the French were mostly defensive in stature and could not really threaten Germany too much. More to the point extensive fortifications didn't figure in their doctrine. Even in the extremely lean times of the 1920s they envisaged mobile divisions counterattacking enemy spear heads as the best way to halt enemy advance.
I looked into two options for how the West Wall resources could have been spent. One army and one navy.
Main resource is armament related ;129,000 tons armored steel and 135,000 tons Stuctural Steel, and the 1.5 billion RM to spend.
Secondary resource is constuction related: 9 million tons concrete with 200,000 tons of rebar plus 170,000 tons of steel girders for dragons teeth and barbed wire etc.
Navy; Naval construction efficency was quite good, with end product equalling about 1/3 of initial input tonnage. But that covers all costs , factory & port related etc at a time when the ship yards were being forced to transition from producing a balanced fleet of surface and subsurface armaments and munitions, to one based mostly on Subs. The actual efficeny on ship construction was on the order of 1/2 to 2/3.
So you end up with about 145,000 to 178,000 tons displacemnt of armored ships from 1937-1940. During this period the naval slow down cost them the
Bismarck Tirpitz Graf Zeppelin &
Peter Strauss, and the three heavy cruisers
Prince Eugen , Seydlitz and Lutzow . There should still be left over tonnage to complete the two planned M class light crusiers, and complete the 9 x Type 1937 Torpedoboot plus 6 -8 x Type 1936 mod Destroyers by 1940. There is still sufficent funding to pay for the construction of about 300 aircraft for these ships , mostly Seaplanes but including some Carrier planes.
The prefered option would be to boost the army , however small tanks are quite wastefull in construction and one can't expect more than 1/3 efficency in input tonnage to out put product. I estimate they could produce ~ 4400 Panzer III/IV type tanks during this time , however the cost of building the 8 additional panzer divisions to house these tanks would be 1.7 billion Rm so a more likely option would be to purchase the 4400 Panzer III/IV [2/3 billion RM] and exchange them with the Panzers I, II & 35/38t in the 10 Panzer divisons raised by 1940 . The displaced 3000 Panzer I/II/35/38t could be reconditioned and integrated into the now motorized infantry divisions in place of either the divisional AtGun battalion or parts of the Recon Battalion. They could even be reconditioned as mechanized guns AKA previous doctrine to give these divisions SturmPanzers/ Panzer Jagers.
The Naval option was proposed to fit in with the ATL of this thread.