I would hardly consider Garratts or Shays to be tank locomotives. Tank locomotives, since they don’t have a separate tender, carry their water in a tank that straddles the boiler. Neither Shays nor Garratts have this feature.
So then this:
would not be a tank engine.
And this:
would not be a tank engine.
Ed
Nor this, either
Locomotives with a tank straddling the boiler are known as saddle tanks and in the UK these are sometimes identified by the suffix “ST” (as in 0-4-0ST).
Locomotives with rectangular tanks attached to the boiler are known as pannier tanks, suffix PT (as in 0-6-0PT)
Locomotives with water tanks contained within the locomotive frames are known as Well Tanks with the suffix WT (as in 2-4-0WT)
Locomotives with rectangular side tanks attached to the frames were simply called tank locomotives with just the suffix T (as in 2-6-4T).
All of these could also have a small water tank on the main frames behind the cab.
The streamlined locomotive in Overmod’s post did in fact have side tanks (small ones) beside the boiler under the streamline casing. But these were supported by the frames, not by the boiler.
The generally accepted criterion is that water tanks are carried on the main frames of a tank locomotive, whether carried by the boiler or not, so both two truck Shays and Beyer Garratts meet the definition of being tank engines.
Peter