The idea is this: Just like the DD and CA pair to make a fairly efficient combo of ships that use a vast number of common parts (even though they can't be converted back and forth), the FF was intended to have a CL companion. This CL would basically look like a scaled-down CA and the saucer would be the same shape and size as the FF.

Federation Alternative Light Cruiser

The resulting CL ends up with a secondary hull about the same size as the saucer, giving it a movement rate of 2/3. It uses 10-point warp engines. Just as with the differences between the DD and CA, the saucer of the CL loses a few boxes in the translation, but is more than made up for in the rear hull. Specifically, in the saucer, the hull is slightly increased, the lab is doubled, and the Ph-3s are improved to Ph-1s, and the aux, tractors, and shuttle are moved to the rear hull.

When the ships were first made, Star Fleet focused on the CA (as the new flagship units) and the FF (cheapest and easiest to spread around). Only after the initial burst of construction did they get around to the DD (really the DDM) and the CL. But, before actually making the CL, they realized two issues:
1) There wasn't much difference between the CL and DD. Plus the Old CL was still around and also about the same level of capability.
2) Unlike the DD and CA, the FF and CL don't share the same engines, removing a key efficiency. (Note that the ships *were* supposed to use the same 10 box engines, but the FF design was easy to modify to use two cheaper engines instead of a single 10 box engine. It was NOT going to be easy to modify the CL to use four frigate engines.)
Because of these issues, the production of the CL was shelved until they could revisit later. As with most such decisions, the revisit never came and the CL was never produced.

Despite that, this ship is still an important footnote as it showed that the Federation originally planned to use two pairs of complementary ships, DD/CA and FF/CL, and had circumstances not intervened, they would have.

By Alex Chobot (Alendrel) on Friday, June 18, 2021 - 06:14 pm: Edit

I like it a lot, as it it does seem like a very logical pairing of classes. My main comments are:

1. I feel the decision on using the two 6-box engines wasn't that they were cheaper (especially as a pair), but that the ship is already so slim on power that the proposed 10-box engine was seen as not viable for the FF.

2. The unrefitted CL-F has less firepower than the DD(M), and after refits the DDG still outguns it (though the CK-F does have more power and a bit more resiliency).

3. Even doubling the labs relative to the FF only gives it 4 labs - half the capacity of the DD(M) and the CA, and thus woefully inadequate by Star Fleet standards, especially for a cruiser. I realize this (and my point 2) is getting into just expanding on your point 1, but I think the differences are more significant than a simple count of boxes or such may indicate.

4. The DD(M) has a YIS of Y130, same as the CA, with the FF going into service in Y127 - so there was no "initial burst" of CAs and FFs with the DD coming along later.

5. The side saucer phasers should be able to fire down the rear hex row like the CA

It's not that it's a bad ship on its own, but it doesn't have a role in Star Fleet's stable. I'd say that such a ship may well have been on the drawing boards, but these issues were noted early enough such that it was never considered to be part of the construction program at any point - it never made it off the shelf in the first, as it were.