Complex sentence: It was designed from the start to be a highly-protected wartime base, and therefore has armoured and underground hangers, and revetments placed close to the runways for aircraft on immediate take-off standby duty.
Split into simpler sentences: It was designed from the start to be a highly-protected wartime base. As such, it has armoured and underground hangers, with revetments placed close to the runways for aircraft on immediate take-off standby duty.