Complex sentence: Beevor, pp.354,355 It is also difficult to destroy underground or heavily fortified structures such as bunkers and utility tunnels; during the Battle of Budapest in 1944 fighting broke out in the sewers, as both Axis and Soviet troops used them for troops movement.
Split into simpler sentences: Beevor, pp.354,355 It is also difficult to destroy underground or heavily fortified structures such as bunkers and utility tunnels. During the Battle of Budapest in 1944 fighting broke out in the sewers, as both Axis and Soviet troops used them for troops movement.