Any Ideas?

I am trying to get some help with identifying this vessel as part of a local archaeology project that I am involved with and was hoping that the combined knowledge through this forum may help.

From what is left, it's a small craft of about 40ft, flat stern section and flared bow which is similar in section to a MGB or MTB. There is the remains of a bulkhead about 2m back, with a further one at about 4m back, before what would appear to be the engine room and then a larger bulkhead at around 8m, with the rear section appearing to be the cockpit.

The construction is all welded metal, which I think rules out most MTB or MGB styles, as does the length.

There are also the remains of 2 portholes on the port side, between the 2m and 4m bulkhead.

There is a distinctive metal bar across the stern, which runs all the way across, about 35cm up, with a central support, made of 5cm tube.

I am wondering if it was some kind of target towing launch or something like that, or possibly a version of an Air Sea Rescue launch.

Any thoughts or ideas which would help idenify this vessel would be greatly appreciated.

And the next one showing the bar across the stern: