GR translation: humped like a dolphin at around caliber 2

[Mike Jing]

V422.35-423.4, P429.34-430.2   . . . watched run after run the
Halbmodelle results out of the wind tunnel, showing how the net normal
force would be distributed over the Rocket’s length, for hundreds of
different Mach numbers—seen the true profile of the Rocket warped and
travestied, a rocket of wax, humped like a dolphin at around caliber
2, necking down toward the tail which was then stretched up,
impossibly, in a high point with a lower shoulder aft of it—and seen
how his own face might be plotted, not in light but in net forces
acting upon it from the flow of Reich and coercion and love it moved
through . . . and known that it must suffer the same degradation, as
death will warp face to skull . . . .

What does "caliber 2" refer to here?
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Pynchon-l / http://www.waste.org/mail/?list=pynchon-l