A military=bunker node can have an additional bunker_type=* tag to specify the exact type of bunker it is. It can be a value from the table below, or some other appropriate value.
A reinforced structure used as a headquarter. For planning, tactics, directing troops and firepower. Often with living quarters and higher ranking officers. Sometimes equipped with observation-decks, periscopes and rangefinders. Not to be confused with the smaller observation post.
A reinforced structure, usually very small, used as a prepared firing position for one or two soldiers. Can be a standalone construction or a part of a trench.
A reinforced structure primarly used for observation and to direct firepower. Differs from a command post, usually a lot smaller and only operated by a few soldiers.
A reinforced structure primarly used for operating and shelter technical installations. Example: Radar, power generators, communication centrals, searchlights.