The Second-in-Command of a smaller group is usually a Captain ( although infantry groups ' Second-in-Command 's were usually Lieutenants until after the Second World War ) , the Second-in-Command of an even smaller group is the Sergeant of the group , and the Second-in-Command of a section is usually a Lance Corporal . The Second-in-Command of a company , squadron or artillery battery ( in which he or she is called the Battery Captain ) is usually a Captain ( although infantry company Second-in-Commands were usually Lieutenants until after the Second World War ) , the Second-in-Command of a platoon or troop is the Platoon or Troop Sergeant , and the Second-in-Command of a section is usually a Lance Corporal .