The Giant Harpoon is a battle item crafted in the Hunter's Lodge.
When enough Giant Harpoons are used on a Titan, it will cause Titan Parts to be dropped, even if the Titan escapes. The level of the Titan will determine the minimum number of Harpoons needed to guarantee a Titan Part drop.
The more Giant Harpoons an Alliance uses on the Titan, the better the drop rate of Titan Parts. The amount of Titan Parts dropped are based on the players' Loot Tier.