one of the first ways of finding the presence of an underwater submarine. The "sniffer" for detecting diesel exhausts was developed in the Second World War. More recently indirect methods of submarine detection have been tried, mainly via its wake. Anti-submarine weapons Anti-submarine weapons can be divided into three categories according to their mode of operation: guided weapons, non-guided weapons, and rocket and mortar weapons. Guided anti-submarine weapons, such as torpedoes, seek out the submarine, either via its own sensors or from the launching platform's sensors. The advantage with this type of weapon is that it requires a relatively small payload as it detonates in direct contact or within a very close proximity of the submarine. The disadvantage is that this type of weapon can be decoyed and is adversely affected by stealth features of the submarine. Non-guided anti-submarine weapons, such as mines and depth charges, are "dumb" weapons that has to be carried to the submarine or that the submarine has to come in close proximity of. This is to some degree compensated by a heavy payload, in some mines exceeding half a metric ton, but since the effect of an underwater explosion decreases with a factor of the distance cubed, an increase in payload of a depth charge from 100 to 200 kg would not result in more than a few meters in killing radius. The main advantage of rockets and mortar weapons, such as anti-submarine grenades and anti-submarine rockets, is their rapid response time as they are carried through the air to the target. Once dropped on top of the target, they also have the advantage of not being sensitive to decoys or stealth features. A hybrid of this category is the rocket launched torpedo, which is carried to the proximity of the target via a rocket; this then reduces the response time and gives the submarine less time to undertake countermeasures or evasive maneuvers. Finally, a submarine can also be destroyed by means of artillery fire and missiles in the rare case that a modern submarine surfaces, but these weapons are not specifically designed for submarines and their importance in modern anti-submarine warfare is very limited. Guns/missiles Gunfire has been used to disable submarines from the First World War onwards, while a helicopter missile attack was used to disable the Santa Fé in the Falklands War. After the First World War, special ASW shells were developed