It's about half as long as The Korean War
In other words, 18 months is 0.48540 times the length of The Korean War, and the length of The Korean War is 2.06 times that amount.(1951-53) (to armistice signing)
The Korean War between North Korea (a.k.a. Democratic People's Republic of Korea, a.k.a. DPRK) and South Korea (a.k.a. Republic of Korea, a.k.a. ROK) began on June 25th, 1950 during the Cold War. The war paused with the signing of an armistice on July 27th, 1953 — 37.08 months — although the war is officially ongoing and marked by occasional border conflicts.
It's about two-fifths as long as The Civil War (American)
In other words, 18 months is 0.3750 times the length of The Civil War (American), and the length of The Civil War (American) is 2.670 times that amount.(a.k.a. War Between the States, a.k.a. the Great Rebellion, a.k.a. the War of the Rebellion) (1861-65) (United States)
The deadliest war in American history, the American Civil War is generally considered to have begun on with the attack on Fort Sumter on April 12th, 1861 and to have lasted until the surrender of Robert E. Lee's army on April 9th, 1865 — 47.90 months. A total of 620,000 American (including Confederate) soldiers are estimated to have lost their lives due to the war.
It's about one-third as long as The First walk around the world
In other words, 18 months is 0.34910 times the length of The First walk around the world, and the length of The First walk around the world is 2.8650 times that amount.(1970 - 1974) (Dave, John, and Peter Kunst) (including time in recovery)
On June 20th, 1970, Dave Kunst set out from Waseca, Minnesota with $1,000 and a mule. Kunst completed his walk around the world (with a four-month pause following an assault he suffered during the journey) on October 5th, 1974 — 51.550 months.
It's about one-third as long as World War I
In other words, 18 months is 0.3430 times the length of World War I, and the length of World War I is 2.920 times that amount.(a.k.a. First World War, a.k.a. Great War, a.k.a. World War, a.k.a. War to End All Wars, a.k.a. WWI, a.k.a. WW1) (1914 - 1918)
World War I is considered to have begun with the assassination of Austrian Archduke Franz Ferdinand on June 28th, 1914 and to have lasted until the signing of the armistice with Germany on November 11th, 1918, for a total of 52.50 months. However, the Treaty of Versailles which ended conflicts between the major powers was not signed until June 28th, 1919 and the last formal peace treaties were not signed until August 23rd, 1923 — 57.40 months after the armistice was signed.
It's about one-fourth as long as World War II
In other words, 18 months is 0.24960 times the length of World War II, and the length of World War II is 4.006 times that amount.(a.k.a. Second World War, a.k.a. WWII, a.k.a. WW2) (1939 - 1945)
The most widespread war in history, the Second World War is generally considered to have started with the German invasion of Poland on September 1st, 1939 and to have until the surrender of Japan on September 2nd, 1945, a total of 72.10 months. Also the deadliest conflict in history, the war had an estimated 60 million casualties globally.
It's about one-fourth as long as The Construction of the Chunnel
In other words, 18 months is 0.23460 times the length of The Construction of the Chunnel, and the length of The Construction of the Chunnel is 4.2630 times that amount.(a.k.a. Channel Tunnel, a.k.a. Le tunnel sous la Manche) (1987 thru 1994) (Folkstone, Kent, UK to Coquelles, Pas-de-Calais, France)
The construction crew of the Chunnel broke ground in England on December 15th, 1987 and the tunnel was inaugurated by the Queen of England and the President of France on May 6th, 1994 — a total construction time of 76.630 months. The 4.9 million cubic meters of chalk excavated from the UK side of the Chunnel was dumped within sea walls to create the 299,467.38 sq. km (74 acre) Samphire Hoe County Park near Dover, Kent.
It's about five times as long as The First artificial heart patient's survival
In other words, 18 months is 4.890 times the length of The First artificial heart patient's survival, and the length of The First artificial heart patient's survival is 0.2040 times that amount.(1982) (Dr. Barney Bailey Clark; first permanent, pneumatic device)
On December 2nd, 1982 Dr. William DeVries implanted the first artificial heart into Dr. Barney Bailey Clark, who went on to live for 3.680 months. This early model of the artificial heart was controlled and powered by an external, 146.51 kg (323 lb) machine that Dr. Clark had to cart with him as he moved throughout the hospital.