Treaty of Algeron The Treaty of Algeron was a peace treaty signed between the United Federation of Planets and the Romulan Star Empire in 2311 , following the events of the Tomed Incident . The Treaty of Algeron was signed approximately 160 years after the conclusion of the Earth - Romulan War . ( ; ) The treaty reinforced and redefined the Romulan Neutral Zone , and made clear that any violations of the Zone without adequate notification , by either side , would be considered an act of war . ( ; ) The treaty also expressly prohibited the development or use of cloaking device technology by the Federation . Then - Captain Pressman attempted to circumvent this clause in 2358 with the test of a phasing cloaking device developed covertly at least in some part by Starfleet Intelligence aboard the . ( ) An exception to the treaty in 2371 allowed for the limited supervised use of at least one cloaking device on loan from the Romulans . Operation of the cloaking device was to be limited to the Gamma Quadrant . In return , the Romulans would receive all information the Federation obtained on the ' s voyages into the Gamma Quadrant , most importantly any information concerning the Dominion . As such , the " Defiant " was the only Federation ship to be permanently equipped with a cloaking device . ( ) However , Captain Benjamin Sisko and his crew violated this amendment on several occasions by using the cloaking device in the Alpha Quadrant . ( , " et al " ) " In Q ' s anti - time future , the Federation possessed and openly used cloaking technology . The Romulan Empire had been conquered by the Klingon Empire , which presumably nullified the Treaty . " ( ) Appendices . Apocrypha . In the video game " " , the Treaty has a provision allowing entry into the Neutral Zone for scientific or archeological purposes , which the " Enterprise " - D exploited to investigate a Chodak planet . Tomalak also appears to reference this provision in In the video game " Star Trek Online " , set in 2409 / 10 , the Romulan Star Empire collapsed due to the destruction of Romulus . The in - game lore however states that the elected president of the United Federation of Planets , Aennik Okeg , proclaimed that the UFP and Starfleet are still bound to the contents of that treaty and all efforts concerning the research and / or developing of cloaking technology have been banned within the UFP ( " The Path to 2409 : Volume 16 , Chapter 2 " ) . This statement was a reaction to the exposed illegal attempts of Starfleet Security to develop cloaking technology of their own when the USS " Kelso " , fitted with a prototype cloaking device , was lost with all hands on Stardate 72487 . 91 due to a critical malfunction ( " The Path to 2409 : Volume 16 , Chapter 1 " ) . Contrary to the games ' own lore , Federation players are able to choose eight ships with cloaking technology , the Refit ( named " Dreadnought Cruiser " in - game ) as seen in , a retrofit of the , battlecruiser , Intel Ships ( Phantom , Eclipse , and Scryer ) , Arbiter , and the Yamato class , which is specifically designed to compete with comparable Klingon vessels . Non - player controlled ( NPC ) versions of those ships however do not show cloaking capability . In the video game , the " Valkyrie " class Federation fighter craft are equipped with cloaking devices .