Aside from hand phasers and phaser rifles, there is another type of phaser used by Starfleet and the Federation - phasers mounted on starships. The following are a few of the phaser classes.
The Type IV phaser is a medium sized device fitted to small vehicles such as shuttlecraft.
As of 2364 the Type X was the heaviest weapon in use aboard Federation vessels, comprising the main armament of the Galaxy class starship.
Previously designated as the Type X+ for security reasons, the Type XII phaser has been used in dedicated planetary defense arrays and as the main armament of heavy fortified starbases since 2363. It was considered that the Type XII was unsuitable for use on a starship platform because the energy requirements of the array where too high and the supporting hardware too bulky. However, by 2368 the power plant of the Sovereign class had grown large enough to support Type XII arrays in place of the planned Type X models; technical improvements had also allowed for considerable shrinkage in the size of the equipment. The main phaser armament of the new Sovereign class starship therefore comprises Type XII phaser arrays as does the armament of the Prometheus class currently under development. These are the most powerful phaser weapons currently in use by the Federation.
Pulse Phaser Cannon
It has long been recognized that the initial impact of a phaser strike on a shield system is the most damaging part of the firing sequence. Many cultures have sought to increase weapon effectiveness against shields by developing pulse cannon - that is, weapons which fire large numbers of tightly packaged bursts rather than a continuous stream. Early Federation vessels such as the Constitution class where equipped with weapons which could fire such pulses, but the weapon is not without its drawbacks; the hardware involved tends to be very difficult to manage precisely, resulting in much poorer control over the beam characteristics. The Federations starship design ethic has always stressed that full control must be maintained over all weapons at all times, in order to allow non lethal force to be used in starship combat situations; in addition, many scientific experiments use weapon systems to apply energy in controlled amounts to external phenomena in order to study reactions. Given this, the Federation gradually moved away from pulse cannon. The refit given to the Constitutions in the 2270's removed the pulse firing feature from that class, equipping them with a 'rapid burst mode' which was something of a compromise between pulse and continuous phaser beams. Further designs continued to de-emphasize the pulse firing feature, although all basic phaser hardware is capable of firing relatively short bursts and this has remained a feature of Federation combat tactics.
With the development of the USS Defiant, the pulse phaser cannon was finally reintroduced to Starfleet. Defiant is a warship, pure and simple; her designers had no real interest in conducting experiments, and the attitude towards the level of lethality of her armament could perhaps best be summed up by the phrase 'take no prisoners'! Defiant's main armament comprises four heavy pulse cannon which fire very tightly confined bursts of phaser energy for maximum impact on shielding systems. High overall energy delivered over a very short period combines with a high firing rate to produce a performance against modern shield systems which can best be described as devastating.
On her first active mission the Defiant faced a group of Dominion Attack Ships; these vessels had successfully withstood several minutes of fire fighting with a Galaxy class starship, but Defiant's phaser cannon cut through their shields within moments. Subsequent combat experience has shown the value of this weapons system, which is currently being developed for use in other vessels.
This information is courtesy of the Daystrom Institute Technical Library and copyright Graham Kennedy.