North American Rocketdyne Designations
Rocketdyne: Powering Humans into Space by Robert S. Kraemer (Pages 110 to 111)
Rocketdyne initiated it’s designation system with the engine for the Redstone, which was called one of three designations:
The A-Series engine (A for first in a series of engines by
The 75K engine (for 75 thousand pounds of thrust)
The NAA-75-110 (NAA for North American Aviation, 75 thousand pounds of thrust, and 110 second burn time)
There were seven different versions of the Redstone engine developed, A-1 through A-7. When Wernher von Braun visited North American to catch up on their current propulsion capabilities sometime in the 1950s, they were currently at the A-4 version for their Redstone engine; something that greatly endeared it to von Braun for obvious reasons.
Because none of the engines for the Navaho missiles went into production, they never received any Rocketdyne designation, beyond their official USAF designation (XLR-83-NA-1, etc) or the thrust level (405K) within the company.
However, when the Atlas ICBM engines were ordered into serial production, the head of Rocketdyne’s Propulsion section, Samuel Hoffman charged Ed Monteath to come up with a continuous numbering/designating sequence for all future engines.
Monteath proposed continuing the alphabetical sequence started with the Redstone engine for all future engines; thus the next production engine would have a “B” designation, and so on.
If his plan had been followed the designations would have been:
B-1: Atlas Booster Engines
C-1: Atlas Sustainer Engines / OR / Complete Atlas Propulsion Package
D-1: Thor Engine
However, the plan wasn’t followed.
According to Ed Monteath, this was due to Sam Hoffman preferring a designation system reflecting the power of the engines, similar to how military piston engines were designated according to how many cubic inches they had – R-4360 or V-1650.
Since Hoffman was in charge, engines within the company were most commonly identified by the thrust level in pounds of the main thrust chamber only (without the contribution of turbine exhaust) for quite a while.
The Monteath sequence did pick up again later with:
E-1: Back up Engine for Titan I.
F-1: Saturn V Booster Engine
G-1: Fluorine/Hydrazine Propulsion System
H-1: Simplified S-3D Booster Engine for Saturn I/IB.
I: Skipped due to similarity of ‘I’ with 1, similar to USAF practices at the time for aircraft designations.
J-2: 200K Hydrolox Second Stage Engine for Saturn IB/V. No idea why it’s J-2 instead of J-1.
L-1 to L-2: Experimental Linear Aerospikes of 100K (L-1) and 200K (L-2) of the 1970s
X-1 to X-8: Experimental Engine(s) used to prove out many ideas for production engines.