The many designs of Kurt Tank

[Lanconic]

Apparently, Kurt Tank had a habit of starting development of 'some' type of prototype
as every different engine became available. In the case of the DB603L apparently the engine had some maint issues that made it difficult to use. But eventually DB solved those issues.

Most of these designs were developed concurrently, not sequentially.

[Hard Sarge]

a few of them did things like this, the 154, never had a "job" it was a design, that then, needed something for it to do, and when the High Command would say, hey we need something to this, Hey, I got a plane I been working on, it would do that easy, they needed a recon plane, they needed a high speed bomber, they needed a heavy fighter, they needed a night fighter

and each time, they needed something, the design would change a little bit more

and yes, agree, a lot of the designs were for a engine was, wasn't ready yet, and when the design got ahead of the game, they would be told to see what it could do, if it used this or that (which, in the long run, all the Nations did close to the same thing)

(and the idea of, hey, lets put a Merlin in it, didn't always work out, the Halli, was a better plane with out it, the P-40 was only so-so, the P-38, looked like a Gem, but they wouldn't shut the production line down, long enough to make the change over (would of taken 2 weeks, test model was a monster)