Former Defense Secretary Donald Rumsfeld has pulled out an unexpected ace from his sleeve: an app to play solitaire. And no ordinary solitaire, this, it is an obscure version that was played by Winston Churchill.

Rumsfeld, 83, learnt the game in the 1970s from Belgian statesman André de Staercke, who was taught by the former British prime minister during World War II, he said in a Medium post.

The game Rumsfeld calls “Churchill Solitaire” is played with not one but two decks of cards, and has 10 rows of cards instead of the usual seven. There is also an additional goal at the end of the game, called the Devil’s Six.

“Churchill Solitaire is not a game for everyone. It takes patience and perseverance, cunning and concentration, and strategy and sacrifice,” Rumsfeld says in the post.

Saying that there were only a handful of people who knew the game now, he realized “there was every chance the game Churchill so enjoyed could be lost to the ages.” He wrote to Churchill’s great-grandson in January 2014 to get his permission to build the app, who was only too happy to lend the family’s name to the endeavor.

The app, available for free download, currently has a rating of 4.5 out of 5 on the Apple app store.