A rough draft from the entry on Phasers that I'm writing for a little project I have going. (The Time frame for the excerpt is 2400)
Phasers have been a part of the Federation Arsenal since it's founding, and while the Phasers of today (Marks 10, 11, and 12, along with the prototype for the Mark 13) bear some resemblance to the Phasers of the 23rd and 22nd Century, to say they're the same as those early Phasers would be dead wrong. While technically, the Phaser was invented just prior to the launch of the Baton Rouge class Starship, for the sake of completeness we in Starfleet Engineering have labeled those Phasers as Phaser Mark 3. Assigning the term (retroactively) to the two models of Phase Cannons in use by Earth and Federation Forces leading up to and during the Romulan War. As the Phaser evolved, we'll note interesting uses, and some strange derivations of it.
The Phaser 1 (Phase Cannons) came into general use just prior to the launch of the NX class vessels. These short lived cruisers were equipped with the Phaser 1 for their entire 15 year life. The Phaser 2 was brought into service for the Daedalus Class Battle Cruiser's Romulan War refit. These improved Phase Cannons were the primary punch for a number of different Starships, while Phaser 1s were still used for defensive purposes. When the Federation mothballed their racial fleets, these Phase Cannons were the primary weapons. Phasers were invented during the mothballing and development of the Federation fleet. The Phaser 4 was developed for the Constitution class's first major refit.
Proximity Phasers: The Phaser 3 and Phaser 4s were capable of firing a Proximity burst. Not too dissimilar from proximity fused Torpedoes, the Phaser energy is encased in a magnetic field that is specially generated to de-stabilize when it gets near a metallic mass. The diffusion of energy made this a very inefficient weapon mode, especially against shielded targets whose shield thresholds are high enough to shrug off that energy with no loss of integrity. However it was very effective against unshielded, and cloaked targets. This firing mode was rendered completely ineffective by two advancements. The first was the development of the 4th generation of Cloaking Devices by the Romulans, that cloak managed to hide their ships from all forms of sensors, making the depth charge firing mode useless. The second was the development of improved targeting and tracking systems that accompanied the Mark 5 Phaser, which made it unnecessary for use against starfighters. Certain aspects of Proximity Phasers would crop up again with the Phaser Cannons.
The Phaser Mark 5 was developed to coincide with the development of the X refit for the Constitution class Heavy Cruisers, taking full advantage of the additional power from the new engines. This represented the biggest jump in firepower from any model Phaser to the next. The Phaser Mark 6 debuted in time to be installed on the Excelsior II class Battle Cruisers, and the Phaser 7 was developed in response to the events that led up to the Tomed Incident. The Phaser 7 was the last fixed emplacement Phaser, although future models would be downgraded to a fixed emplacement to keep older vessels up to date.
Phaser Cannons: In response to the Klingons developing their burst firing Disruptor Cannons, Starfleet built these as an experiment. In a classic example that is repeated throughout history, Perception was more real than reality. The power of the Phaser Cannons was never up to par with their standard counterparts, sometimes having as much as an 15% loss in damage output. But it was hard to get their first reported use out of the public mind. The Phaser Cannons were being prototyped on the USS Miranda's shakedown cruise. During the shakedown, the crew reported a 32% power reduction (adjustments would be made following the incident to bring the Mark 5-c up to 89% of the Mark 5) between the Mark 5-c Phasers, and the Mark 5 Phasers. Unknown to the crew of the Miranda at the time, their shakedown cruise was being watched by the IKV Hegh'Moh. The Hegh'Moh was on a mission to test their new Cloaking Device against Federation border sensors. They penetrated without being detected and stumbled upon the Miranda's shakedown. The Hegh'Moh was under strict orders to not engage, and to withdraw upon detection. The release of documents from the Klingon Empire sheds a little more light on this incident. Apparently the orders were worded as such, that if fired on first, the Hegh'Moh was free to return fire at the Captain's discretion. The High Council believed, as discovered in their after action report, that any Federation Captain, if they discovered them, would ask at least one "naive, annoying and rhetorical" question before opening fire, and as such they felt that adding the words, "if fired on, you may respond in kind", would assuage the Captain of any sting the orders to not engage under any other circumstances may have provided, but not provoke an interstellar incident. The Hegh'Moh remained on station observing the Miranda, but they were not as hidden as they thought. A junior lieutenant noticed the Hegh'Moh while calibrating the Miranda's new sensors. She re-calibrated her sensors three times and ran a diagnostic twice, when she reported her findings to the Captain, they all thought it was something curious about their sensors, and fired one of their six Photon Torpedoes to confirm that it was indeed a sensor problem, when the Torpedo struck a K't'inga class Battlecruiser, everyone involved was shocked, then the Hegh'Moh returned fire. During the battle, the Hegh'Moh had gained the upper hand in large part because the Miranda had only five Torpedoes left. With the Miranda's shields went down, she had no choice but to use every weapon at her disposal, including the balky Phaser Cannons. When the Phaser Cannons opened up on the Hegh'Moh for the first time, a portion of it's firepower passed directly through Klingon's shields. Shocked, and not wanting to risk losing their ship, the Klingons cloaked and left the area. In hindsight, the whole incident might well have been comical, if not for the loss of 32 people on the Miranda and 14 on the Hegh'Moh. But the perception of the Phaser Cannons being the new super weapon took hold in the Federation Council, which ordered as many ships as possible to be outfitted with these new weapons. Starfleet Engineers advised against it, and did their best to keep the weaker Phaser Cannons from being deployed through out the fleet. After the development of Phaser Arrays with the Mark 8, Starfleet Engineers thought that they had finally put the overrated Phaser Cannons to bed once and for all.
The debut of the Ambassador Class Heavy Cruiser also marked the next big jump forward in Phaser technology since the Phaser 5. The Phaser 8 brought with them an Array of Phaser Emitters, that increased the firepower of one shot with a much wider firing arc. What 3 Phaser Mark 7s covered, it only took one Mark 8. These Phasers weren't more powerful because of any individual performance increase, but because they clustered 3 to 5 emitters into one array and fired all of the emitters in one concentrated beam. During the Cardassian War the Mark 9s were rolled out, but their major improvement was an improved cooling system, that allowed the Phasers to fire more quickly than the Mark 8s. The Phaser 10 debuted with the Galaxy Class Starship, but were quickly uprated to Phaser 11s after the Wolf 359 incident. As with the 8 to 9 upgrade, the 10 to 11 upgrade saw a marginal increase in firepower, but also the ability to rapidly change resonance frequencies to better adapt to Borg Shields, without having to wait until the ship's shields were down because the quickly shifting shield frequencies would stop the beam and damage the firing ship.
Pulse Phasers: Also in response to the Wolf 359 incident, the old Phaser Cannons were brought back up to the SCE. The SCE quickly brought the old Cannons up to Mark 11 specs, but were hesitant to order a fleet wide refit because the Mark 11-p lost the ability to arrange their emitters into an array. They found a perfect test subject in the USS Defiant, a ship highly maneuverable (something almost all Federation Ships were lacking at this point), and still in the early stages of its construction. The Defiant performed so well in the Klingon-Cardassion War II, and the early Dominion encounters, that more ships were built, and the Mark 12-p was authorized along with the standard Mark 12s.
The current Mark 12 Phasers are a by-product of the Dominion War. In the build up for the war, it was determined that a fleet wide refit was in order to counter the power of the Dominion Polaron based weapons, and the Mark 12s came into production mere weeks before the outbreak of the war. As of this writing a new Phaser being developed is the Mark 13, it is still in the early prototype phase, with Engineers having trouble adapting the Mark 13 for use in an array setup.
Take from it what you will, I just thought I'd share it.