Please note: Much of what follows conflicts with numerous published sources. I am aware of this, and I believe this information to be correct.
A little terminology:
Armored Cruiser is the same as First Class Cruiser
Protected Cruiser is the same as Second Class Cruiser
Peace Cruiser is the same as Third Class Cruiser, or a large Gunboat
Light Cruiser is defined by the London Treaty as a cruiser with guns of less than 6.1 inches
Heavy Cruiser is defined as a cruiser with 6.2 inch to 8 inch guns.
Old Designation System: Pre-1920
Prior to 17 July 1920, USN ships were given designations in the form Battleship 4 or Cruiser 8. There were no official abbreviations for these designations, but some abbreviations were commonly used.The pre-1920 cruiser classifications were as follows:
Cruiser (C-) A single series for Protected and Peace Cruisers.
Armored Cruiser (ACR-) All Armored Cruisers were numbered in this series.
Scout Cruiser (CS-) Fast, lightly armed scouts were in this series.
Battle Cruiser (CC-) Large, heavily armed Capital Cruisers
Unnumbered Cruisers A few Protected and Peace cruisers were not given designations/numbers.
1920 Reclassification
On 17 July 1920 the entire designation system was thrown out and replaced.The new desigations established were the following:
Cruiser (CA) For all older, slower ships.
Scout Cruiser (CL) For all fast scouting ships.
Battlecruiser (CC) Same as original Battlecruiser classification.
Cruiser Minelayer (CM) For minelayers converted from cruisers.
The old Cruiser designations were split up as follows:
Peace Cruisers (C-) were changed to Gunboats (PG) with new numbers.
Protected Cruisers (C-) became Cruisers (CA) with new numbers.
Armored Cruisers (ACR-) became Cruisers (CA) with their original numbers.
A few Protected Cruisers (C-) that had been converted to minelayers became Cruiser Minelayers (CM) with new numbers.
One Unnumbered Protected Cruiser became a Cruiser (CA), and some Unnumbered Peace Cruisers became Gunboats (PG)
When all this was completed, the old Cruiser designations were completely gone and all ships classified as cruisers were in the Cruiser (CA), Scout Cruiser (CL), Battlecruiser (CC) or Cruiser Minelayer (CM) series. Because development of the CM series diverges from cruiser development after the first two ships, CMs will not be traced as part of the evolution of cruiser designations.
1921 Reclassifications
On 8 Aug 1921, several additional changes were made in the cruiser designations. The Scout Cruiser (CL) designation was redefined as Light Cruiser (CL) to include old Peace Cruisers and some Protected Cruisers. All surviving Peace Cruisers, classified as Gunboats (PG) in 1920, became Light Cruisers (CL), receiving new numbers. Two Protected Cruisers, classified as Cruisers (CA) in 1920, became Light Cruisers (CL). They retained their previous numbers.With the 1922 suspension, and eventual cancellation, of the Battlecruisers (CC), all remaining cruisers were either Light Cruisers (CL) or Cruisers (CA).
1931 Reclassificatons
In the late 1920s, a new series of lightly armored, 8-inch gun cruisers had been started. These ships were designated as Light Cruisers (CL). The London Treaty defined a Light Cruiser as having guns of 6.1 inches or less, and a Heavy Cruiser as a ship with 6.2 inch to 8 inch guns. Thus, the new 8" ships had to be redesignated. This was done on 1 July 1931, with a large number of Light Cruisers (CL) becoming Heavy Cruisers (CA). These ships retained their numbers. The old Cruisers (CA) were essentially gone, so duplication of the CA designation was not a problem.From this point forward, Light Cruisers (CA) and Heavy Cruisers (CA) were numbered in a single series. A single Cruiser (CA) remained in a separate series, but she had been reduced to a hulk in 1927.
Changes Through the 1940's
On 17 Feb 1941 the last old Cruiser (CA) became an IX, finally eliminating the Cruiser (CA) series. With this change the Navy had only one cruiser series: CL/CA.The first Alaska class ship was laid down in 1941, designated in the Large Cruiser (CB) series. This series was completely separate from the CL/CA series.
On 18 March 1948 a group of Light Cruisers (CL) became Antiaircraft Cruisers (CLAA), retaining their original numbers and remaining part of the CL/CA series.
In 1949 the designation Hunter-Killer Cruiser (CLK) was established. This designation was numberd independently of the other cruiser designations. CLK did not last long, with the last ship becoming a Frigate (DL) 9 Feb 1951.
Guided Missile Cruisers
The new guided missle cruiser series was established 4 Jan 1952. The designations eventually included the following:Guided Missile Cruiser (CG)
Nuclear Powered Guided Missile Cruiser (CGN)
Guided Missile Light Cruiser (CLG)
Guided Missile Heavy Cruiser (CAG)
These ships were numbered in a single series, separate from other cruiser series.
Two ships were given guided missile classifications while numbered in the CL/CA series: one as a CLG and one as a CLGN, later changed to CGN. They were renumbered into the guided missile series on 28 May 1958 and 1 July 1957, respectively.
The 1975 and 1980 Reclassifications
On 30 June 1975, several designations were altered:Guided Missile Light Cruisers (CLG) became Guided Missile Cruisers (CG), and a group of Guided Missile Frigates (DLG/DLGN) became Guided Missile Cruisers (CG/CGN).
Finally, on 1 Jan 1980, a group of Guided Missile Destroyers (DDG) became Guided Missile Cruisers (CG).