Military organizations tend to detach personal for long shifts so the remaining unit can stay somewhat functional in their normal schedule. When I was on guard

Military organizations tend to detach personal for long shifts so the remaining unit can stay somewhat functional in their normal schedule. When I was on guard duty it was usually a 24h shift followed by a 24h break for a group of 8 or 10 privates and 2 NCOs. That means that roughly a quarter of the company is permanently detached. If you switch to 12hour shifts, you have to consider that normal operations take place during daytime. At any day you then have three groups unavailable: One on duty, one resting from the night shift, and one preparing for the night shift.