Okay ... I found some of the meanings listed. They don't tell me the "form" of punishment though. I do know that losing pay and detention happened. But what were they made to DO while being punished? Were they just locked in a cell to twiddle their thumbs or put to work?

jankers
noun

1. military., slang
Punishment, detention, etc for defaulting.

glasshouse
noun

1. A building with walls and roof constructed mainly or entirely of glass, and with the internal temperature maintained at a constant predetermined level, used for growing plants which need special protection or conditions.
2. slang
A military prison.

Karmen.