I'm not sure that the Bob Semple tank deserves the flak it gets, if you consider the context.

When was it produced?

kagis

https://www.amusingplanet.com/2021/11/bob-semples-tank-new-zealands-homegrown.html

Work began on a prototype at the Temuka PWD Depot in June 1940.

By March 1941, a second tank was finished, and both took part in a parade in Christchurch. One was then sent to Wellington and then on to Auckland to promote the war effort.

So they started June 1940, and while they don't say when the first one was done, but we're into 1941 to get something else out.

So, here's the situation that the Kiwis are facing, because I think it's maybe easy to forget that.

The UK has been badly-beaten in Europe, and may well be conquered in short order.

The UK, the major security provider for New Zealand, has just been overwhelmingly defeated on land in Europe. While many people in the British Expeditionary Force were pulled off in a desperate operation, the British land warfare equipment has been lost, and is largely in the Reich's hands. It is not at all clear that the UK will not surrender or be defeated in short order. Prime Minister Winston Churchill had just given his "We shall fight on the beaches" speech:

Even though large tracts of Europe and many old and famous States have fallen or may fall into the grip of the Gestapo and all the odious apparatus of Nazi rule, we shall not flag or fail. We shall go on to the end. We shall fight in France, we shall fight on the seas and oceans, we shall fight with growing confidence and growing strength in the air, we shall defend our island, whatever the cost may be. We shall fight on the beaches, we shall fight on the landing grounds, we shall fight in the fields and in the streets, we shall fight in the hills; we shall never surrender. And even if, which I do not for a moment believe, this island or a large part of it were subjugated and starving, then our Empire beyond the seas, armed and guarded by the British Fleet, would carry on the struggle, until, in God's good time, the New World, with all its power and might, steps forth to the rescue and the liberation of the Old.[10]

So he's just raised the likelihood that the UK is about to be invaded. He has raised the possibility that the UK may fall, and that in that scenario, the "Empire beyond the seas, armed and guarded by the British Fleet, would carry on the struggle", which probably means that land warfare is up to them, along with the remnants of the Royal Navy. That means New Zealand, a tiny country with a then-population of about 1.6 million and not a whole lot by way of heavy industry, much less defense industry. He's telling them to hang on and hope that the New World -- that'd be the US -- intervenes.

Also, keep in mind that even if that happened, while the US had a decent navy, it had a tiny army by European standards then. Germany, while not possessing much by way of a surface navy, had a much larger land army than the US. The US was not going to be doing a great deal on land in the near term, even if it became involved.

That's a pretty heavy burden for a nation with a population a seventh the size of London that was mostly a bunch of farmers.

That's the context in which they're starting work on what makeshift armor they have the ability to produce out of what hardware and industry they have available.

The US will not enter the war for another year-and-a-half. Over 1940, the UK is being bombed in the Battle of Britain, and suffering major shipping losses.

https://nzhistory.govt.nz/war/second-world-war-at-home/challenges

From early in 1940, New Zealanders began to live in fear of attack or invasion, first by the Germans and later by the Japanese.

By May 1940 the Germans occupied Norway, the Netherlands, Belgium and France, and Britain faced the direct threat of invasion. Although appalled by events on the other side of the world, New Zealanders still felt far from the danger zone. But the sense of security was short-lived. German raiders, or armed merchant cruisers, were active in New Zealand waters, laying mines and attacking Allied ships. Their targets were the vessels that sailed to or from the country, transporting troops, freight and passengers. The raiders had some success: in the second half of 1940 they sank four ships in the seas around New Zealand, with the loss of more than 50 lives.

The Germans had other targets in the Pacific. The tiny island of Nauru, a British Commonwealth territory north of the Solomons, exported thousands of tons of phosphate each year to New Zealand, Australia and Britain. The chemical was essential to fertilise farms and grow much-needed food. But German raiders had the phosphate ships in their sights, sinking five of them in early December. The prisoners they took brought the total captured in the Pacific to nearly 700 in the space of six months.

Members of the EPS practise first aid

Then, on 27 December 1940, the German raider Komet bombarded Nauru Island itself, destroying the phosphate plant. The attack provoked a stir in New Zealand. The Defence Force galvanised the Home Guard into action, and civilian authorities also prepared for the worst. Before the war began, the government had devised the Emergency Precautions Scheme (EPS), the forerunner of Civil Defence, to cope with disasters. 'Enemy action' was one of the possible dangers listed in a 1939 EPS booklet, sent out to local authorities. Now, it was decided, the time had come to confront that menace.

The blackout began in coastal areas of New Zealand in February 1941. Black curtains, paper, or even paint, covered windows in most homes. Street lighting was dimmed, making life difficult through the winter nights that followed.

The US would not become involved until the end of 1941, and at that time, its Pacific Fleet suffered a tremendous blow at Pearl Harbor, with many of its major fleet units knocked out of action. Japanese forces were successfully invading and occupying British, Dutch, and American territories all over the Pacific. That's a dangerous neighborhood to be in.

This is the Pacific Theater.

In Europe, open areas and road and rail infrastructure meant that much heavier tanks were in use. In the Pacific Theater, often far lighter tanks were made use of; light tanks and tankettes could make a major difference where they weren't facing heavier vehicles. The US benefited significantly from the amtrac in amphibious assaults, which had even lighter armor than the Bob Semple tank.

https://www.battleforaustralia.asn.au/Tanks_Guadalcanal.php

The ground, and in particular the tank battle was fought by US Marines. Guadalcanal was possibly the first deployment of allied tanks in the jungle (the Japanese had effectively used light and medium tanks in Malaya), in the course of the action in the Solomon Islands the Marines learned the need to protect tanks (particularly light ones) in close country. The lesson was costly but when applied the Stuart (only one made it to the point of battle) was the bunker buster essential to victory in the last major incident of the campaign.

That is a single light tank being used there.

If you find yourself in a situation where you need to move over open ground against, say, a machine gun, even a slow, lightly-armored, lightly-armed tank sure beats a WWI-style trench warfare massed charge. And that's the kind of alternative that the Kiwis might have had available to them, not loads of Shermans or whatever.