In the late 2280s, Starfleet began to experiment with ways of increasing energy through-put in both shipboard and planetary phaser banks. The first model to make it past the testing stage and enter field service was the FH-X-1 Large Aperture Phaser Turret (nicknamed the "Thunderbolt").
The LAPT concept used a single oversize turret to take the place of the then-conventional twin-mount turrets in most other heavy phaser banks. The expanded nadion chamber and large-bore firing aperture permitted a larger beam emission per second of release time, and boosted output power by 25% during the testing phase.
The larger turret was not physically steerable, however, and as a result, LAPT mounts were limited to covering a single 90 degree arc (45 degrees left or right of the turret centerline based on the location of the mounting hardpoint chosen. Beam redirection was accomplished by use of a modified ACB system to channel the nadion release.
In actual service, the FH-X-1 and it's slightly larger immediate follow-on system the FH-X-1-A, received mixed reviews from the ships it was incorporated into. The increase in effective firepower was welcome, but many captains felt that the aiming limitations unnecessarily straightjacketed their tactical options. Either they had to accept the reduced coverage at the edges of their aiming arcs, or their ships had to be refit with the so-called "plus 4" turret pattern on the primary hull (as used in the Excelsior class), which reduced internal volume available for other purposes slightly to accommodate the additional hardpoints, power transfer systems, and so forth.
In addition, the ACB beam-management system proved to be somewhat touchy, and required regular maintenance to maintain the required jacketing focus. Failure to maintain a LAPT properly (or if one were damaged) had a tendency to result in both a reduction in output power due to beam "bloom" as well as a tendency to "firehose" the emission, which resulted in a loss of accuracy.
In the end, the FH-X program was considered at best a moderate success. No refinements past the 1-A model were authorized, and service was generally limited to use in planetary defense batteries, on large orbital facilities that could afford the extra space to offset the targeting problem, and by certain classes of ship that required a high-output phaser capacity, namely battlecruisers and battleships.
Starfleet shelved the idea of ACB-directed phaser banks for over half a century, when advancements in technology made the concept more practical, and led to the development of collimator array phaser banks in the mid 24th century.
---Jane's Defense Quarterly, Spring 2366 edition
