The chronology for Prime Directive's version of the Starfleet universe uses an Earth-based calendar with dates given in "Y-years" dated to the year Earth first made contact with the Vulcans (termed Y0. These events were shown in the Next Generation film "First Contact"). 
Direct conversion to familiar Anno Domini dating is difficult to work out exactly but Y0 should be somewhere between AD 2020 and AD 2090 depending on the chronoilogy used (various games, books, the TV shows and the films all use ever so slightly different systems for the First Contact date, meaning Star Trek canon is riddled with chronological inconsistencies).

In our campaign the date of First Contact follows that of the Film as it is the medium most known by the group. Y0 is therefore set at 2063 and follows the Amin-Audeh Chronology. Happy Cochrane Day.

The SFU defines the "five-year mission" of the USS Enterprise A (NCC-1701-A) from the original Star Trek series as being from Y155 to Y160.

The Chronology of the Starfleet Universe is split into eras. These are shown below with key dates defined in each era under their subheadings to make it easier to understand the Chronology and the campaigns place in it.

Non-Tactical Warp Era
-Y129 – Vulcans develop warp drive. 
Y0 – Zefram Cochrane (with the assistance of the time-shifted crew of the Enterprise E) operate the first manned Warp drive flight. This leads to First Contact with the Vulcan race.
Y1 – Humans develop the first fully operational warp drive.
Y11 – Kzintis develop warp drive for the first time.

Early years
Y62 – Human and Vulcans invent Tactical Warp drive, enabling starships to engage in combat and safer defensive postures while travelling faster-than-light. Up until this point ships in warp were highly vulnerable to damage while travelling FTL.
Y79 – Tholians first arrive in the Milky way, fleeing their own galaxy.
Y80 – Tholians start colinising the outer rim of the galaxy, infringing on Klingon space while Klingons are engaged elsewhere.
Y84 – Klingon/Lyran offensives start the conquering of Hydran space in earnest
Y87 – Hydrans overcome by the Klingon/Lyran offensives other than three 'Lost colonies'
Y92 – Klingons start retaking territory from the Tholian invaders
Y102 – Klingons are defeated at the Tholian Dyson-sphere homeworld after a decade long campaign to push the Tholians back. 
Y113 – Sixteen Orion ship crews mutiny and disappear. These crews become the nucleus for the Orion Pirates
Y116 – A Kzinti civil war ends when the Usurper (leader of one of the two warring factions) sends his ships into an energetic nebula, rather than face capture by his enemies. The Usurper finds the nebula is actually hollow and used the area  to set up a government in whay becomes known as the WYN Cluster

Middle years
This is the era of The Original Series which is set in Y154 – Y159. It starts in Y120 with the introduction of the first 'normal' ships (e.g., not prefixed by a letter to designate its era in the game designations). Technology and borders are fairly constant through this era, but several important things do happen.

Y130 – The Federation colony Aurora disappears in a massive ion storm. It has actually been transported to the Omega octant where it becomes the capital of a minor interstellar state. 
Y135 – The Hydran lost colonies build an all-new fleet and retake the old Hydran Kingdom in a surprise campaign against the Klingons and Lyrans.
Y155 – USS Enterprise syarts it's 5 Year mission. 
Y158 – The Four Powers War begins. This war involves the Klingons, Kzintis, Lyrans and Hydrans in the biggest armed conflict yet seen. The Klingons and Lyrans form a Coalition and the war goes their way until the tide of war changes with the introduction of Hydran Helbore Torpedoes and Kzinti starfighters.
Y162 – The Four Powers war ends with a peace treaty maintaining the status quo. All powers in the Alpha Octant realise nothing has changed and that a re-ignition of the war is inevitable. The next decade is dedicated to improving starship technology in preperation. 
Y166 – The first Andromedan ships are encountered.

The General War
Y168 – The Lyrans and Klingons attack the Kzinti Hegemony. The Hydrans pre-emptively strike the Lyrans and Klingon Coalition fearing they would be next to be attacked. This action starts the General War.
Y169 – The Hydran capital falls
Y170 – The Coalition assaults the Kzinti homeworld. The Federation starts preparing to intervene on behalf of the Kzintis. 
Y171 – With war against the Hydrans and Kzintis wrapping up, and the Federation mobilizing, the Klingons invade the Federation
Y173 – Klingons convince the Romulans to join the Coalition. 
Y174 – The Coalition drives deep into Federation space. The Gorn Confederacy joins the Federation-led Alliance and help stabilise the Klingon/Federation/Romulan borders. 
Y175 – The situation becomes a large-scale stalemate with both sides fighting back and forth in "devastated zones" that have been denuded of pre-war bases. The superior Federation economy, and the toll of several years of war prior to invading the Federation, cause the war to slowly turn in the Alliance's favor. 
Y178 – The Hydrans recover and make a drive back to their capital in Y178
Y179 – Federation and Gorn fleets make a strike into Romulan space
Y180 – First "X-Technology" ships start to appear
Y181 – federation and Gorn fleets cause the devastation of the Romulan secondary capital, Remus. 
Y185 – A cease-fire that leaves the original borders of the major powers mostly intact is agreed with all parties thoroughly exhausted from the lengthy wars

ISC and Andromedan invasions
Y185 – The ISC decide to save the other Alpha Octant races froim themselves and start the "Pacification Program" or "ISC Conquest", in the hopes that if the conflicting factions could be kept apart wars could be prevented.
Y188 – ISC forces reach Lyran space on the far side of the Alpha Octant and have spread everywhere in 'peacekeeping' duties
Y188 – Start of the full-scale Andromedan invasion.ISC forces decimated due to being so spread out on peacekeeping missions.  All the major powers of the Alpha Octant put under great pressure in their weakened states from the General war. 
Y195 – Secret of the Andromedan transportation network discovered.
Y201 – All Alpha Octant  powers (led by the Federation and Klingons working together) counterattacked the Andromedans in Operation Unity, which traced the Andromedans back to their main base in the Small Magellanic Cloud. 
Y202 – Andromedan invasion halted by the destruction of the the starbase in the Small Magellanic Cloud and the removal of their capability to easily travel into the Milky Way 

Trade wars
Y204 – Second generation of X-ships start to appear in Federation, Romulan and Klingon space.
Y205 – Trade wars begin 
Y210 – Alpha Octant is invaded by the Xorkaelians from the Omega Octant
Y225 – Third generation of X-ships start to appear. This is the timescale of The Next Generation series.


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