STANLEY MCCHRYSTAL’S voice is hoarse as he addresses a packed arena in Helsinki. His audience, mostly businessmen in dark suits, is rapt. The American former general tells thrilling battlefield stories of leading the Joint Special Operations Command in Iraq, which captured Saddam Hussein and killed Abu Musab al-Zarqawi, al-Qaeda’s local chief. He explains how his outfit adapted against an unexpectedly difficult enemy. A change in management style let his group go from conducting a handful of raids each month to hundreds, achieving better results against insurgents.

Neither America’s occupation of Iraq nor Mr McChrystal’s military career ended well. He went on to lead Western forces in Afghanistan, but stood down in 2010 after falling out with his political bosses. He reinvented himself as a management consultant. His McChrystal Group employs 65 people. It draws on its founder’s experience hunting insurgents to advise businesses, including on Wall Street, on corporate culture.

What insight does an old soldier offer? Mr McChrystal is an apostle of devolved responsibility, or letting junior employees know and do more. One convert is his host in Helsinki: Reaktor, a 17-year-old firm of 400 staff, mostly coders, with a side-interest in launching satellites. An employee, Mikko Olkkonen, explains that “we have no hierarchy, no bosses, no targets, no quarters.” It heeds Mr McChrystal’s approach: firms can adapt in complex competitive environments, he argues, only if information is shared and teams of capable staff—not just the boss—can take decisions. It also helps greatly with recruiting to say that junior staff will have clout early in their careers.

A variety of big firms are listening. Mr McChrystal sits on the board of JetBlue Airways and of an American subsidiary of Siemens, a German engineering company. His firm advises Barrick Gold, a Canadian miner; Under Armour, a sportswear brand; a large bank; and several hospitals. Any assignment begins with “discovery” by an intelligence analyst who previously assessed the organisational structure of al-Qaeda. She works out who takes decisions inside companies. The reality usually differs from formal organisation charts.

“The management ideas I believe in are not revolutionary, but I came at it from a different experience,” says the ex-general. He says firms should break apart “silos” and get employees talking. Mr McChrystal’s advice on devolved power has its limits—no army, after all, has done away with hierarchies entirely, and even decentralised al-Qaeda was weakened by removing its leaders. It is hard to know how much his big corporate clients use the approach in pursuing sales and markets. But hearing an ex-general disparage hierarchies so forcefully thrills employees. Even as a Reaktor staffer explained in Helsinki that Finns rarely idolise heroes, the crowd sent Mr McChrystal off with an excited ovation.