Complex sentence: In 2002, Northrop Grumman and Lockheed Martin were working on the development of a 30,000-lb (13,600 kg) earth-penetrating weapon, said to be known as "Big BLU", although funding and technical difficulties resulted in the development work being abandoned.
Split into simpler sentences: In 2002, Northrop Grumman and Lockheed Martin were working on the development of a 30,000-lb (13,600 kg) earth-penetrating weapon, said to be known as "Big BLU". But funding and technical difficulties resulted in the development work being abandoned.