(Reuters) - Boeing said on Thursday it hired former Northrop Grumman executive Colin Miller to head its Phantom Works research arm within the company's defense business unit.

Miller's hiring as general manager of Phantom Works at Boeing Defense, Space and Security (BDS) had been in the works before the arrival of new Boeing CEO Kelly Ortberg.

Boeing's defense business has been struggling under the weight of budget-busting older contracts, but Ortberg said in October that the unit which makes helicopters, fighter jets and missiles remains "core" to the company's future.

Miller's hiring was first reported by the Wall Street Journal.

(Reporting By Allison Lampert in Montreal)