Operation Jackroot was a top-secret program started by the Gudersnipe Foundation during the Kamian Succession Wars. The program involved building freightors and cargo-haulers that could deceive Kamian sensors and appear as capitol-class starships. While officially "classified", the scope of the program was so large that it really could not be kept much of a secret; but because it was so effective in its primary goal, the Kamian knowledge of it could not underride the program.
Early in the war, during the Battleship Crisis, the Foundation pressed into service many retrofit cargo ships augmented with weapons systems left over from obsolete warships. Called "scrappers", these ships had extremely questionable value as warships, and were largely relegated to escort duties. Against all odds, the scrappers proved highly successful. Any conflict usually went poorly for the ad-hoc vessels, yet in every convoy they were assigned to protect, the odds of a Kamian attack dropped by half, or more.
At this point, the Foundation discovered two things about the Kamians: they had no intelligence network to speak of, and their long-range sensors were not very good. The Kamians did not know about the scrappers, and when they scanned the supply convoys at long range, the shape and arrangement of the ships led the Kamians to believe that they were fully-armed warships.
With this in mind, the Foundation spun up a program to capitalize on these defficiencies by building supply ships and troop transports that were specifically designed to look like (and appear on sensors as) warships.
Code-named Jackroots, these ships fell into two categories, called "mockups" and "semis".
A mockup was just an empty shell placed over a fairly standard freightor, and equipped with systems that mimicked weapons arrays. The Foundation had ways of creating uranium shadows and shorting power conduits to make the "hat" appear on sensors as a heavily armed warship. They were cheaply made and should not have been very effective; in fact, the idea had occured to the Foundation before the war, but never been implemented because the disguise could not fool Foundation sensors. Kamian sensors, it turned out, were much cruder than expected, and the ruse worked.
Early mockups went over existing transports, but later in the war they began building customized ships that could do the job more effectively while still remaining inexpensive. Some of the more elaborate mockups even split in half, to make loading and unloading of standardized shipping containers easier.
Semis were much more dangerous to Kamians and entered a little later in the war. These ships looked like large dreadnaughts externally, and employed the same kind of technology that made the massive gun turrets appear functional, while really packed with supplies. The Semis, however, held a surprise for any Kamians foolhardy enough to assault them: while the guns were fake, the ships carried full missile and torpedo systems, on par with the ships they mimicked. While they lacked armor and the rigid structures of actual battleships (to make room inside for more supplies), the wapon systems gave them serious teeth, and many small Kamian raiding parties were fooled into attacks.
By the early mid-war, the Foundation had fielded enough mockups and semis to cause Kamians serious problems. Since Kamian tactics relied heavily on disrupting supply lines, their plans became unexpectedly risky. A Kamian invasion, relying on long-range sensors, could not tell if they were facing a lightly-armed supply convoy or a heavily armed fleet. To make matters even worse, the Foundation frequently mixed actual battleships with the jackroots, which complicated the matter.
This rather effectively stalled out the war, and kept the Kamians rooted for some time.
In at least one instance late in the war, the Foundation sent a massive fleet of Jackroots along with a single task force (roughly 10 jackroots for each warship) to route a Kamian offensive. The gambit was successful, without a single shot being fired.
The Foundation continued to build and deploy jackroots after the war, though their effectiveness was considered highly questionable. Any foe with a good intelligence network could easily determine which ships in a convoy were and weren't actual warships.