Here is a specific example from their site.
The infantry was/were guarding the bridge.
So I can choose either was or were. My question is whether the meaning is exactly the same. If there is a slight difference in meaning or nuance could you please explain what it is?
Five hundred infantry was marching to the north.
Five hundred infantry were marching to the north.
Five hundred infantries were marching to the north.
Are they have the same meaning?