Summary: This is really well designed LEGO vehicle. I previously bought the Shellraiser set for my son and while that one was cool, it was really fragile. The walls on the shellraiser were basically 1x2 or 1x3 connections from the base to the roof. This turtle sub is definitely designed to be much sturdier. The joint for the "neck" of the sub is well reinforced.
Summary: This set was missing vital pieces that we were not able to replace from the many other lego sets we have purchased in the past. I did not want to return it because my grandson is so close to completing the build. I had to order the pieces from Lego.