Complex sentence: In some navies the medium to large sized helicopters have been deleted in others they have been retained for operations from carriers and land bases, they form for example the main anti-submarine strength of the British, Spanish and Italian carrier air wings.
Split into simpler sentences: In some navies the medium to large sized helicopters have been deleted. In other navies they have been retained for operations from carriers and land bases; they form, for example, the main anti-submarine strength of the British, Spanish and Italian carrier air wings.