Answer:
Patroclus becomes distraught by the plight of his fellow soldiers, as the Trojans close in on their position Patroclus helps the wounded soldiers and then the old general Nestor begs him to convince Achilles to join the fight and turn the tables.
Achilles refuses but Patroclus still dtermied convinces Achilles to let him wear his armour and thereby fooling the Trojans into thinking Achilles has returned.
Patroclus appears and the Trojans glee and the Greeks are inspired, Patroclus shows himself to be a fine warrior and slays Sarpedon the son of Zeus.
Unfortunately things don’t go too well after this, he reaches the walls of Troy going against Achilles instructions. Apollo the patron God of Troy intervenes and Patroclus is surrounded by Trojan troops and eventually killed by Hector the prince of Troy.
Before dying he promises Hector that Achilles will avenge him, there is then a fierce battle over his amour and body his body is regained by the Greeks but Hector gets his armour.
So to conclude, Patroclus wears armour as he is upset by the plight of the Greek troops and wants to help. Achilles allows this on the terms that Patroclus not go too far and only allows this because of his love for his companion.
