Quantcast Chapter 11 - Alignment

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For any weapon system to be effective, the destructive device must be delivered to the target accurately. Many air targets are now capable of speeds faster than sound; therefore, they must be detected and engaged at greater distances. Technological improvements in modern weapons systems require that equal improvements be made in their associated detection and fire control systems. Proper battery alignment is a must if ordnance is to be delivered on target.

In this chapter we will describe the basic fundamentals of alignment principles and battery alignment. We will also discuss firing cutout mechanisms, radar alignment, and the final alignment and test.


LEARNING OBJECTIVES: Describe alignment principles and procedures on naval gun systems.

The elements of a modern combat system must work together with a great degree of accuracy to deliver ordnance on target. All are electrical y and/or mechanically linked to pass data from one unit to the next. Each equipment with alignable properties must be aligned to a common reference to ensure a correct exchange of data between the various systems. Data transmission and response synchros must be properly zeroed. All gun bores, missile launchers, fire control directors, radar antennas, gyrocompasses, and other similar pointing lines must be parallel (when no parallax or ballistic corrections have been made). Combat system alignment is the process of establishing parallelism, within acceptable tolerances, between the elements of the combat system.

In this section we will describe the sequence used in establishing combat system alignment. Following that, we will discuss the more familiar sequence of alignment verification.


Combat system alignment begins with the design of the ship. Alignment is established as the ship is constructed. Once constructed, alignment is continually perfected up to the point where the ship is placed in commission and its permanent operational crew is on board. As a ship goes through its normal life cycle, it is the job of the crew to verify this alignment continually, making corrections as necessary.

Certain steps in a combat system alignment process must be accomplished according to a specified sequence. The sequential steps are as follows:

1. Establishment of reference planes

2. Establishment of reference marks

3. Establishment of parallelism

4. Performance of fire control radar radio frequency (RF)-optical alignment

5. Performance of train and elevation alignment

6. Establishment of benchmark and tram reference readings

7. Performance of dynamic train alignment

Establishment of Reference Planes

The first major alignment step is the establishment of reference planes. A position can only be described by relating it to a known reference point. Reference planes allow combat system elements to be described as to how they are situated in relationship to each other. Reference planes are established during the initial construction of the ship and are used as required during alignment of the combat system. Reference planes consist of the center-line reference plane (CRP), the ship base plane (SBP), the master reference plane (MRP), and the weapons control reference plane (WCRP).

CENTER-LINE REFERENCE PLANE.- The center-line reference plane (CRP) is the first plane established. It is the plane containing the ship's center line and is perpendicular to the SBP. The CRP is the reference used to establish the train zero alignment of all of the combat system equipment.

SHIPBASE PLANE.- The shipbase plane (SBP), the basic plane of origin, is perpendicular to the CRP and includes the base line of the ship, but is not necessarily parallel to the keel.

MASTER REFERENCE PLANE.- The master reference plane (MRP) is a plane within the ship parallel to the SBP. On most ships, the MRP is represented by a master level plate that has been accurately leveled to the SBP and aligned in bearing to the CRP. The MRP is used as the machining reference to establish the foundations of the combat system equipment. After initial construction alignment, the MRP is only used as a reference plane following major damage or modernization.

WEAPON CONTROL REFERENCE PLANE.- The weapon control reference plane (WCRP) is established during initial construction and is usually represented by the roller path plane (RPP) or the equipment that has been designated the alignment reference. This is the plane, which most people are familiar with, that is involved with alignment verification. On the FFG-7 class ship, for example, the WCRP is the roller path of the Mk 75 gun mount.

Establishment of Reference Marks

The second major alignment step is the establishment of reference marks. Reference marks include center-line reference marks, offset center-line reference marks, and equipment bench marks.

CENTER-LINE REFERENCE MARKS.- Center-line reference marks are established during initial construction to represent the ship's center line. Several small plates (at least two forward and two aft) will be installed at intervals along the center line to indicate its location.

OFFSET CENTER-LINE REFERENCE MARKS.- Offset center-line reference marks are also established during initial construction to facilitate the combat system alignment. The offset center line is established parallel or perpendicular to the ship's center line. These marks are installed to prevent repeating the center-line survey during subsequent alignments. They must be maintained within 1 minute of arc of the CRP.

BENCH MARKS.- Bench marks are the most familiar of all the reference marks to the average equipment operator/maintenance person. A bench mark is installed for each equipment that has an alignment telescope. Bench marks are installed at any convenient location that is visible through the equipment telescope.

Equipment bench marks are used throughout the life of the ship to verify alignment.


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