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The only evidence that there was ever a plan to fly this in space is a minor source otherwise undocumented. It is one man's fantasy -- more science fiction than real space history. The section should be deleted or greatly reduced in length. 70.215.57.84 ( talk) 21:03, 29 July 2016 (UTC) reply

Several articles here explain that HL stand for Horizontal Landing. I have read that it stood for Heavy Lifting, to contrast with the M2F2 et al. — Preceding unsigned comment added by 2001:8003:E414:3A01:38EF:CEFA:F7EB:A5E ( talk) 06:54, 9 October 2020 (UTC) reply