The Bob Semple Tank was not that bad.

First off, we are going to assume that it would have gotten its 37 mm cannon attachment like how the designers wanted.

Second we are not going to compare it to Panthers and Tigers because those are heavy tanks and Bob Semple is a light tank. (this is an even worse version of saying the Sherman was bad because it couldn’t penetrate German Tanks.)

Let’s start with the armor. Yes it might look like roofing material but it was 8-12mm steel which would be adequate against Japanese Rifles and light to heavy machine guns. Grenades are a possibility to damage the tank even though they won’t penetrate because they would damage external equipment. Now the real problems would be the type 97 anti-tank rifle according to New Zealanders it would have survived but 12mm would definitely not defend against 20mm type 97. However this rifle was quite rare and on top of that heavy. Conclusion is there wouldn’t have been many encounters and it wouldn’t guarantee a kill even in an encounter. Now for the type 94 37mm anti tank gun yeah no Bob ain’t surviving that.

Now against Japanese tanks the type 95 Ha-Go and type 97 Chi-Ha. For the type 95 its 37mm would kill a Bob however it had armor of 8-25mm which the Bob would have been able to penetrate. So against Type 95 it would be who scores a hit first wins but the Bob had low mobility and how high it was the type 95 scores first most of the time. Same goes for the type 97 can kill a Bob but can also get killed by it with type 97 scoring first most of the time. Yes the Japanese had other ways to take out tanks like direct artillery planes and mine lungers.

So in conclusion against a 1941 Japanese landing force the Bob Semple would have been atleast have C tier effectiveness and the Kiwis would have a form of a tank to use rather than having none.