Bethesda's Fallout Shelter was proved rather fruitful for the publisher.
The game was globally the fourth best-selling iOS game in June, according to app analytics firm App Annie.
But it was King's AlphaBetty Saga that claimed the top spot.
Fallout Shelter was announced on-stage at Betheda's conference at this year's E3.
In its first two weeks on the App Store, Fallout Shelter made $5.1m in revenue, according to data firm SuperData. Within days of launching, the game topped the App Store charts in 48 countries.
Bethesda's marketing boss Pete Hines has said the title is set for release on Android in August.