> To what extent did the navy co operate in providing escorts for these army vessels? how were any such escorts arranged?
It was decided by the negotiation of the army and navy. The central negotiation was made by GF and General Army and the local negotiation was made by fleet and army.
In Nov. 1943, the Escort GHQ was established in the IJN and it managed the escort duty.
> did the IJA ever provide there own escorts...I remember reading about army "aircraft carriers" for escort use.
Basically, the escort was the duty of the IJN. But, in the late of WWII, the ability of the navy escort declined and the IJA built some escort vessels.
> I know that some specialised vessels were built to transport landing craft...were these ordered by the IJA?
> and if so to what extent was the IJN involved in their design?
IJN was not involved.