Destroids were a series of non-transformable battloids used by United Earth during the First Robotech War. They were heavily armored and some had superior firepower to Veritech fighters but lacked the maneuverability of the versatile Veritech, which saw them used mainly for support and defensive missions. (Robotech Infopedia)
The development of Destroids began after the Macross Incident in 1999 as part of the United Earth military's preparations for facing an attack by the creators of the SDF-1. These efforts were part of Project Excalibur, which began in 2001 with the first successful series, the Destroid Tomahawk entering service in 2006. They were deployed alongside VF-1 Valkyries. (From the Stars: "The Gathering Storm")
First Robotech War
Post-First Robotech War
Behind the scenes
The Destroids, when released as toys by Matchbox, had new names; Excalibur, Spartan, Gladiator, and M.A.C. II. The original line of RPGs based their mecha entries after those, but with the reboot, each mecha had its name restored.
For the Robotech II: The Sentinels series, the intent was to have new versions of the destroids: the Excalibur MK VII, Spartan MK XII, Raidar X, Gladiator MK III, and M.A.C. III. The Raidar X is the only one of these than has not been used in any known primary or secondary sources. The rest held appearances in the Robotech II: The Sentinels comic series. The M.A.C. III also had a cameo in Robotech: Love Live Alive, making it the only Sentinels Destroid to appear in Primary Canon. A page in Robotech II: The Sentinels: Book 2 indicates that the REF carried first-generation Destroids aboard the SDF-3, although that could be an art error.
The Robotech RPG series later made more Destroid designs based off of those, although none of those have been brought into Primary or Secondary canon at all (as no media has been released since their creation). These include the prototype also called the Defender, M.A.C. Mini-Monster, Gladius Destroid, and Crusader Destroid.
The latest Palladium Books roleplaying sourcebook Robotech: Expeditionary Force Marines Sourcebook One introduces new Destroids used by the Robotech Expeditionary Force: ADR-05-Mk. XIV Defender, MBR-12-Mk. II Valiant, HWR-02-Mk. VII Monster, MBR-05-Mk. X Tomahawk, MBR-08-Mk. VI Spartan, and SDR-05-Mk. XV Phalanx.