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Did NASA use metric or English units for Project Mercury?

For example, did they measure delta-v in meters/second or in feet/second?

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Project Mercury used imperial units of measure. For example, the Mercury spacecraft main instrument panel indicated altitude in FT (feet):

   the Mercury spacecraft main instrument panel

   The Mercury spacecraft main instrument panel from Project Mercury Indoctrination, May 1959 (Source: NASA. Click for full size)

They used statute miles as a measure of distance in schematics, diagrams and other vectors in the documentation, for example this Proceedings of a Conference on Results of the first U.S. manned suborbital space flight from June 6, 1961:

   First U.S. manned suborbital space flight - pictorial presentation of the overall flight

   First U.S. manned suborbital space flight - pictorial presentation of the overall flight (Source: Public archive (in PDF format))

And even went at length to provide their personnel travelling abroad (in this case Mexico) with unit conversion tables from the imperial to the metric system of units in NASA's Introduction to project Mercury and site handbook:

   Chapter 6, Page 13 extract from the Introduction to project Mercury and site handbook

  Page extract from the Introduction to project Mercury and site handbook, notes on personnel travels to Mexico (metric system of units)

Imperial units of measure persisted throughout the Mercury program. This is the mission timeline for the Mercury-Redstone 4, launched on July 21, 1961:

T+ Time     Event                Description
---------------------------------------------------------------------------------------
T+00:00:00  Liftoff              Mercury-Redstone lifts off, onboard clock starts.
T+00:00:16  Pitch Program        Redstone pitches over 2 deg/s from 90 deg to 45 deg.
T+00:00:40  End Pitch Program    Redstone reaches 45 deg pitch.
T+00:01:24  Max Q                Maximum dynamic pressure ~575 lbf/ft² (28 kPa).
T+00:02:20  BECO                 Redstone engine shutdown - Booster Engine Cutoff.
                                 Velocity 5,200 mph (2.3 km/s)
T+00:02:22  Tower Jettison       Escape Tower Jettison, no longer needed.
T+00:02:24  Craft Separation     Posigrade rockets fire for 1 s giving 15 ft/s (4.6 
                                 m/s) separation.
T+00:02:35  Turnaround Maneuver  Spacecraft (ASCS Automatic Stabilization and Control
                                 System) system rotates spacecraft 180 deg, to heat 
                                 shield forward attitude. Nose is pitched down 34 deg 
                                 to retro fire position.
T+00:05:00  Apogee               Apogee of about 115 mi (185 km) reached at 150 mi (240 
                                 km) downrange from launch site.
T+00:05:15  Retrofire            Three retro rockets fire for 10 s each. They are 
                                 started at 5 s intervals, firing overlaps. Delta-V of
                                 550 ft/s (170 m/s) is taken off forward velocity.
T+00:05:45  Retract Periscope    Periscope is automatically retracted in preparation 
                                 for reentry.
T+00:06:15  Retro Pack Jettison  One minute after retrofire retro pack is jettisoned,
                                 leaving heat shield clear.
T+00:06:20  Retro Attitude Man.  (ASCS) orients spacecraft in 34 deg nose down pitch, 0
                                 deg roll, 0 deg yaw.
T+00:07:15  .05 g Maneuver       (ASCS) detects beginning of reentry and rolls 
                                 spacecraft at 10 deg/s to stabilize spacecraft during 
                                 reentry.
T+00:09:38  Drogue Para. Deploy  Drogue parachute deployed at 22,000 ft (6.7 km) 
                                 slowing descent to 365 ft/s (111 m/s) and stabilizing 
                                 spacecraft.
T+00:09:45  Snorkel Deploy       Fresh air snorkel deploys at 20,000 ft (6.1 km). (ECS) 
                                 switches to emergency oxygen rate to cool cabin.
T+00:10:15  Main Para. Deploy    Main parachute deploys at 10,000 ft (3.0 km). Descent 
                                 rate slows to 30 ft/s (9.1 m/s)
T+00:10:20  Landing Bag Deploy   Landing Bag Deploys, dropping heat shield down 4 ft 
                                 (1.2 m).
T+00:10:20  Fuel Dump            Remaining hydrogen peroxide fuel automatically dumped.
T+00:15:30  Splashdown           Spacecraft lands in water about 300 mi (480 km) 
                                 downrange from launch site.
T+00:15:30  Rescue Aids Deploy   Rescue aid package deployed. The package includes 
                                 green dye marker, recovery radio beacon and whip 
                                 antenna.

Units are also converted into metric system for convenience, original mission communications transcript is available here (in PDF format).

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  • $\begingroup$ Apollo displays were imperial, but the systems used metric and converted for the convenience of the crew $\endgroup$ – JCRM Jul 17 at 11:12

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