Sam Bishop was a member of UNIT.
Though he came from a family of bookkeepers and teachers, Sam was inspired to join the military as a child by his great-grandfather, who would regale him with stories of when he fought with the Eighth Army in North Africa during World War II, serving in battlefronts such as El Alamein, Tobruk, and Gazala.
With UNIT, Bishop often went on dangerous missions. Kate Stewart sent him on a mission to the Gobi Desert to track an Energy unit. On this mission a set of Autons attacked him. He was then sent to Puerto Rico to track the Nestene energy units landing. (AUDIO: Earthfall)
He sent Kate and Colonel Shindi to Black Archive 5, as there was something useful in the vault. (AUDIO: Armageddon) When he came back to the UK he was supposed to meet with Kate, but he missed her as she was on her way to Geneva. He helped Josh to realise that the Tengobushi killed Anna Burges to get information on where Osgood was going. (AUDIO: Death in Geneva)
On Kate's orders he followed Felicity Lyme to Antarctica and discovered her facility in there which was generating enough electricity to supply the British Isles. He posed as coming from an energy company to find this information. He managed to get the other territorial powers on the continent to show a power of strength against Bergam's forces. (AUDIO: Ice Station Alpha)
He thought that Kenneth LeBlanc was idiotic. After hearing both Kate's and Osgood's memories about the incident at Helena Faversham, he decided to investigate further. He looked at the CCTV footage of the raid and convince Kate that it had happened. He then helped Osgood to invesigate the people who McGee said had visted the house. (AUDIO: Square One)
He had to deputise for Carter when he went AWOL. He found the footage in the moon landing telling the humans to kill the silents on sight. He then went with Osgood to find out where Carter had sent a set of explosives. Going with Kate and Osgood to LeBlanc constituency count, he took a set of troops to destroy the Silents there and disarm a bomb. (AUDIO: Silent Majority)
He went with Osgood to the UNIT satellite to fix something on there, but they were knocked unconscious upon arrival. He explored the space station and discovered that the crew had been killed. Due to the Silents editing his memory he forgot this and aided Osgood to finish her mission. He decided to get Osgood and himself off the station piloting the Suez capsule. (AUDIO: In Memory Alone)