I've had this Revell 1/144th Beluga kit in my stash for several years but put it off because the decals had yellowed - the submarine idea struck me when I was turning the box & saw the art upside-down.
I started assembly with the fuselage halves - as with any large fuselage (or submarine hull) look at putting tabs inside to strengthen the long joins - failure to do so will result in often cracking them open when handling - especially on a pear-shaped airplane such as this ! After a year of considering this build, I decided to not go with a working whale-tail or the wing-mounted azo-pods for propulsion as I had a submarine kit for another project that provided the horizontal tail-planes & a double propellor -- (that project will use most of the spare parts from the Beluga).
So after sealing up the fuselage, I mounted a drop-tank as a sonar-pod on, what is now, the lower fin & fitted an extra fin on the top. I cut down the wings, glued some sprue in the open ends & puttied/sanded to shape as sponsons and that is the main build & under-coating done.
Still need to drill holes & fit several detail items & do the final painting (needs more yellow & some red trim) & add some decals, if I can fnd something suitable ....