Sons of war heroes record one American soldier holding on (7)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

EP (abbreviation for extended-play record) + I (one in Roman numerals), then GI (American soldier) holding ON . In Greek mythology, the “Seven against Thebes” died heroically in battle, and then their sons (known as the Epigoni or “descendants”) started another war a few years later to avenge their fathers. No, I didn’t know that, but the wordplay made a plausible-looking Greek word and Wikipedia confirmed it.