Editing Project HARP (section)

=== Martlet 3 ===
The Martlet 3 series consisted of advanced rocket-propelled projectiles. They were built and tested for the HARP project but were ultimately not successful due to restrictions in funding and a severe lack of technical information regarding large rocket grains' behaviour under high acceleration loading. When testing these projectiles, the danger of in-bore detonation was considered a severe potential problem.<ref name=":11" />

==== Martlet 3A ====
The Martlet 3A was an {{convert|18|cm|in|adj=on}} diameter, gun-fired rocket projectile that theoretically could reach 500&nbsp;km altitude. As HARP's first attempt at a low-cost sabotted rocket system, the projectile was built with [[fiberglass]] or aluminum bodies. A standard 6-inch rocket was bonded to an aluminum case. The rocket nozzle was supported by a pusher plate, which would impart the missile's acceleration through the aluminum wall casing. Fiberglass limited acceleration to 3600&nbsp;[[standard gravity|g]] (corresponding to a velocity of {{convert|3800|ft/s|m/s}} at rocket ignition). The Martlet 3A's original objective was to carry a 40-lbs payload to an altitude of 500&nbsp;km, which theoretically was feasible if the system could be launched at full gun pressures. The rocket motors' solid propellant deformed during firing and the design was never successful, despite several test firings.<ref name=":11" /><ref name="astronautix2">
{{cite encyclopedia
 | title= Martlet 3A
 | encyclopedia= Encyclopedia Astronautica
 | publisher= astronautix.com
 | url= http://www.astronautix.com/lvs/marlet3a.htm
 | access-date= 2016-01-22
 | url-status= dead
 | archive-url= https://web.archive.org/web/20160304000121/http://www.astronautix.com/lvs/marlet3a.htm
 | archive-date= 2016-03-04
}}
</ref>

==== Martlet 3B ====
The Martlet 3B was similar to the Martlet 3A but using steel casings and attempting to solve some of the 3A model's other problems. The casings survived {{convert|5100|ft/s|m/s}}, but the propellant failed at {{convert|3400|ft/s|m/s}}. This was solved for later rockets by filling the propellant cavity with liquid, but only after developing the 3B model had ended.<ref name="astronautix2" />

==== Martlet 3D ====
The Martlet 3D model was planned as a suborbital test rocket, using the first stage of the Martlet 4 solid rocket version. As the Martlet 4 was never built, no Martlet 3Ds were produced either.<ref name="astronautix2" />

==== Martlet 3E ====
The Martlet 3E was a solid suborbital rocket designed to be fired from a smaller, 7-inch (180&nbsp;mm) cannon used in the HARP project. Its basic concept revolved around packaging the rocket grain in a case with elastic properties to transmit the lateral strain to the gun tube. The 3E model utilized a new rocket grain construction technique that consisted of laminating sheet double-base propellant grain under hydraulic pressure.<ref name=":11" />