上操 is a military verb-object compound meaning 'to go out for drill' or 'to do military exercises'. It's a separable verb (离合词): when you need to add a duration, frequency, or aspect marker, the object 操 splits off from the verb 上 — for example, 上过一次操 ('did drills once') or 上了三个月的操 ('did drills for three months'). You can also use the measure word 次 between the syllables to count occasions.