Complex sentence: However on April 25 the "Santa Fe", after a successful supply mission to the island, was spotted by a Westland Wessex HAS.Mk.3 anti-submarine helicopter from HMS "Antrim", and attacked with depth charges.
Split into simpler sentences: However on April 25 the "Santa Fe", after a successful supply mission to the island, was spotted by a Westland Wessex HAS Helicopter: anti-submarine. Mk.3 helicopter from HMS "Antrim", and attacked with depth charges.