Best way to get a unique artillery piece in an unit?

[Dili]

This device(a 381mm gun turret) only appear after war start and is unique so will not be in production. The unit exist from war start.

I thought of 2 potential solutions:

A - Have that device in pool from start, the unit will have 2 TOE's and the last one have that device at correct date.

B - Unit have only one TOE, arrive with 0 in that device and the device arrives in correct date by a Convoy - this prevent the use of 2 TOE's requiring only one.

Any alternatives ideas or mistakes or wrong assumptions foreseen?

[m10bob]

Of course you are referring to the editor?
Yes, I would put one in the pool from the beginning, and one withing the TOE of the unit itself.
Historically were there others in the world, and if so, were any others manufactured?..If not, make them obsolete in january 1942 and do not allow the one in the unit to be replaced by anything but what really replaced it.

I had to do this to replicate some historical fortress's on Corregidor and the CONUS west coast.

[Dili]

Yes editor. One was put in Genova in 1942. There were others 15" there in Brindisi, Siracusa-Augusta(Sicily) and Venice.

Large calibers i think there were also some German, including a 406mm, likewise there existed a 406mm in Leningrad, Soviet Union.

French had some 340mm.