Here's a sample of the kind of news you get if you sign up for Jane's Defence email briefings. It's annoying that you can't read the whole story without a paid subscription.
Japan seeks further HALO systems
Japan's Ground Self Defence Force (JGSDF) is looking to buy 15 more BAE Systems Hostile Artillery LOcator (HALO) systems after successfully completing the evaluation of a single system, originally ordered in 2002.
It seems that HALO is a "battlefield-wide system for collecting acoustic signals from many types of source and combining the data in a number of ways [including but not limited to] for computing the position of guns, mortars and shell bursts on the battlefield"