Complex sentence: Meanwhile, the 12th Light Horse Regiment established all round defensive positions, including picquets guarding the pumping station which were withdrawn at 23:00, when brigade headquarters arrived, and took over garrisoning duties.
Split into simpler sentences: Meanwhile, the 12th Light Horse Regiment established all round defensive positions. The picquets guarding the pumping station were withdrawn at 23:00, when Brigade Headquarters arrived, and took over garrisoning duties.