The UK’s Brimstone smart missile system is getting smarter. The government has awarded missile makers MBDA a £400 million contract to extend Brimstone’s service until at least 2030. But some are worried that incremental upgrades could give Brimstone the capabilities of an autonomous weapon , such as the ability to make decisions about where to look for targets by itself.

Brimstone missiles have been used since 2005 and can be launched from aircraft, helicopters and drones. They are used both as standard laser-guided missiles, …