This is the 4.5-inch howitzer that goes with the Crompton's Emplacement Destroyer 3 (ED3). Scale is 1:72. It still in the early stages, despite my having started it several years ago. I made only one wheel for this build. I tried to make the box trail open, but the card is way to delicate for that; maybe in a larger scale...
The spoked wheels are a B!+[h to make. Each wheel is made of two halves, each of which is laminated (double-thickness). The two halves are glued back-to-back after they are cut out. I originally tried to cut out a 4-sheet lamination, but it was too hard to cut the spokes out. Individual spokes would have been impractical at this scale. I also considered a solid 2-ply core and a single ply printed and cut-out on each side, but I didn't like not being able to see through the spokes.
The ED3 will feature a partial howitzer in case the modeler wants to complete it with the doors closed.
Here are photos of the Crompton ED3 alpha build in progress. The interior is a bit tricky to line up the inner and outer panels so it all fits without racking. #738 shows the right-side engine and an internal sidewall stiffener. #739 shows the left rear. I considered making the roof out of individual plates like the original, but it would have been way too fiddly. I'm making the roof flat, then I'll shade it to simulate the lapped plates. #740 shows the open front with the 4.5-inch howitzer in place. The gun is a tight fit with the shield top in the upright position.
As I design the cardmodel, some practical matters come to mind. The original concept design seems to omit ventilation intakes, view ports or a commander's cupola, defensive weapons, fuel tank, storage for the howitzer's wheels and ammunition storage. I might make a "gray" model as the concept, plus a more practical version as it might have been if it had reached service - with all the items listed.
Here are two more photos of the Crompton Emplacement Destroyer 3 (ED3) build in progress. This is the full model, with interior. When I am finished with it, I will adapt the pieces to make a version with the doors closed - no interior. The first one (#748) shows the interior before attaching the top and sides. Since taking this photo, I have adjusted some of the interior pieces.
The second (#749) shows attaching the bottom of the hull. The sides and top are already attached. The hull is made of three main pieces that overlap so that there is a printed surface inside and outside. I will take photos of the colored beta build as part of the instructions.