Which tank was the worst tank ever built?

No one particular tank can be accredited as being the "worst tank ever built" because if it was; it never would have been built and put into service to begin with. Therefore all military tanks put into eventual military service met the "standard" of those particular times for those particular services. However...tanks that had the following characteristics eventually were considered obsolete or having non-acceptable qualities:

1. Soviet (Russian) BT tanks were powered by gasoline, diesel was safer.

2. German Tiger & Panther tanks; poorly built (constructed with haste) and suffered from continuous breakdowns (unreliable-not properly field tested).

3. United States M4 Sherman tanks used gasoline, diesel was safer.

4. Any armor (tanks) built using rivets as a primary method of assembly was inferior to welded armor.

The best tanks were: Reliable, Durable, Easy to Produce, Easy to Maintain, Easy to Operate, Used Diesel Fuel, and had adequate guns & armor.