Gibbs...we hardly know ye

The Season 3 premiere and finale, "Kill Ari" and "Hiatus" respectively, have raised big questions about the continuity of the Leroy Jethro Gibbs storyline from Seasons 1-2. Wives, years at NCIS, previous agents, odd behavior - what is going on with Gibbs?

The discrepancy has prompted jokes about aliens, robots, and alternate realities. Here is the Gibbs timeline, with Seasons 1-2 side by side with the different information provided in Season 3.

The greatest discrepany has been over the issue of Gibbs marriages. Go here for a breakdown of what is going on with all the Mrs. Gibbs-es.

With a heartfelt thanks to the Friends of NCIS and the NCIS Special Ops boards. I am particularly indebted to posts by ceindreadh and DC for most of this. My special thank you to the NCIS agent and member of "FoN" (NavyWife), who now advises the show, for her help with some of my questions.
 

(This chart runs on the assumption that one season is roughly one year. This is based on several comments made during the series. Thanks to DC.)

• "Yankee White" aired 23 September 2003. In "The Curse", which aired 28 October 2003, Kate says she has been at NCIS for one month.
• Kate has been at NCIS one year when "Lt. Jane Doe" airs on 19 Oct 2004.
• Tony says in "Meat Puzzle" (08 February 2005) that six months have passed since they first saw the puzzle ("Reveille", 24 May 2004).

	Seasons 1-2	Season 3 and on
USMC	Gibbs is a MP; sniper abilities vague Gibbs was a military policeman at Camp Lejeune and broke up many fights at Court Street, "J-ville", but was one of the nicer guards ["My Other Left Foot"]. His background as a sniper is vague. He asks Kate ("Secret Service") where to locate snipers in the Gitmo camp when they track down their killer ["Minimum Security"]. When they give the mm count for the bullet which killed a recruiter, Gibbs do not immediately place the caliber with what kind of weapon is used; Kate does, saying it is a rifle. It is not until Abby adds that the bullet went through several things and the shooter had to be long range does Gibbs realize it is a sniper ["One Shot, One Kill"]. Our only indication he was a sniper come from his ability to do land navigation ["One Shot, One Kill"].	Gibbs is a sniper He recognizes right away the caliber of the bullets and the rifle used to kill Kate. He used a Marine M-40 A-1 sniper rifle with hand-loaded, Lapua, .308, boat-tail, full metal jacket, molybdenum-coated bullets. (Ari used the same kind of ammunition with a Bravo 51 - a "Kate".) ["Kill Ari"] He displays his prowess with a rifle several more times, including when he revenges his family's death ["Hiatus"].
1982		Gibbs marries first wife, Shannon.
1984	Gibbs joins NCIS. He has spent nineteen years "doing this" - generally interpreted as being a NCIS agent, although a small minority consider it simply interrogating (compatible with his MP experience, but not with his sniper experience) ["Ice Queen"] This explains the NIS tee-shirts.	Gibbs is still in the Marines. His daughter is born.
1988-90		Gibbs does a tour in Panama as a sniper. The Marines were in Panama from '88 through '90.
Desert Storm goes from August 2, 1990 to February 1991. Five months of war in 1990, two months in 1991.
1990	Gibbs is commanded by Col. Ryan during his time at Desert Storm. Lt. Cameron dies in his arms "fourteen years" before 2004, putting his death in 1990 ["Engima"]. There are five months of war in 1990. There is no mention of his family. This is not incompatible with his time at NCIS. A real-life NCIS agent said in an interview that many agents who are reservists are called to active duty when a war begins, leaving the agency a bit shorthanded. They simply return to their civilian NCIS job when their service is over, just as any other reservist does.
1991		Gibbs is deployed in 1991, his family is killed, and he walks into a minefield. (The war ends in February 1991). He ends up in a coma. He returns home, hoping for justice for his family. When none is forthcoming, he goes to Mexico and kills the killer himself. Unfortunately, the scene itself is inconsistent. Shepard says the daughter was born in 1984 but was eight years old when she died, making her death the earliest in 1992 - after the Gulf War was over. Gibbs joins NCIS in August ["Hiatus"]. The problem is in "Honor Code", Kelly wore a NIS tee-shirt - before her father joined the agency.
1992	The NIS becomes the NCIS.
1992-1995	The Bosnian War goes from 1992 to 1995. NATO peacekeepers enter afterwards on a peacekeeping mission until 2004.
	A colonel makes reference to Brcko, and Gibbs says that he saw that expression on the colonel's face in Bosnia. Marriage #2 is over by this time. The colonel says that he heard Gibbs has "remarried again" - meaning that Gibbs most likely had already remarried and divorced for the first time (second marriage) by the time he meets the colonel ["Eye for an Eye"]. (This does not exclude the possibility they may have had a meeting sometime in the decade after their first and the colonel discovered Gibbs had divorced #2 then.)
1996	Gibbs is in Washington, D.C. His newest agent is Stan Burley, who has just left his job as a senator's aide and will work with Gibbs for five years. We know Stan began in 1996 because Tony inherits Burley's desk - there is no agent between them - and Tony has been at NCIS two years when the series begins in 2003 ["High Seas", "The Curse"]	Gibbs is in Washington, D.C. He is tracking a serial killer, and his capture of the man gives Agent Cassidy - a college student at the time - her first peaceful, fearless night in months ["Mind Games"].
1999	Gibbs is stationed in Washington, D.C., still mentoring Stan Burley. He is hit on the head by Wife #3, whom he soon divorces. During this last divorce, he is chasing a child molester, whom he does not catch for one year. Ducky is an intimate witness to Gibbs' behavior and failing marriage during the child molestation case ["The Curse", "Reveille"]	Gibbs is stationed in Europe, where he has a fling with Agent Jennifer Shepard ["Kill Ari"].
2000	The USS Cole is bombed at a Yemeni port while refuelling.
	Vivian Blackadder arrives any time at the end of 2000 through 2003, applying to NCIS after her brother is killed on the USS Cole ["Ice Queen"]. Quite possibly she came to NCIS before Tony did; she could have joined Gibbs' team before Tony did, also, but given Gibbs' behavior towards her this is unlikely.
2001	Stan Burley leaves. Tony arrives and "inherits" Stan's desk ["High Seas"]
2003	We meet the team, April 2003 [Ice Queen]. Viv Blackadder leaves Gibbs' team, and possibly NCIS, between April and the end of September. Kate Todd joins Gibbs' team at the end of September.