Japan is sending its first troops to a combat zone since World War II, as a small humanitarian force set off to deploy in Iraq.
The troops will be heavily armed to defend themselves
"Yours is a very noble mission," Defence Minister Shigeru Ishiba told the 30 soldiers on parade in Tokyo.
They are the advance guard of a 1,000-strong force due to arrive by March.
Japan's constitution bans its soldiers from fighting overseas and there are fears that the troops could get drawn into combat in Iraq.
The soldiers leaving on Friday are due to arrive first in Kuwait for training, where a team of 20 Japanese air force staff has been making preparations since last month.
They will then deploy in the south Iraqi town of Samawah - a largely peaceful part of Iraq - where they will help restore water services, offer humanitarian assistance and help rebuild schools and other infrastructure.
PACIFISM UNDER THREAT?
Japan's constitution renounces the use of force
This has been stretched to allow self-defence troops
1992 law allowed troops to join UN and relief work overseas
2003 law said troops could go to non-combat zones in Iraq
PM Koizumi wants to give Japan even greater powers
In all, 600 ground troops and 400 air force and naval personnel are due to be deployed.
In Japan, government offices, nuclear power plants, airports, railway stations and US facilities have all been on a security alert ahead of the dispatch, which has caused controversy and raised fears of terrorist attacks.
About 100 demonstrators protested outside the defence ministry in Tokyo during Friday's departure ceremony.
Surveys suggest that at least two-thirds of the Japanese public are opposed to the plan with critics arguing that the mission violates the post-war constitution, in which Japan renounced war forever.
An apparent threat from al-Qaeda aimed at Japan, reported in an Arabic newspaper late last year, has also raised security concerns regarding its operation in Iraq.
However, the BBC's Jonathan Head in Tokyo says the deployment seems irreversible and attention has turned to revising the constitution so that Japan can in future contribute more easily to multinational military operations.
Prime Minister Junichiro Koizumi has defended his decision to send troops, saying that Japan will never earn what he calls an "honoured place" in the world if it refuses to risk the lives of its servicemen abroad.
The country was criticised for contributing only money, not troops, after the 1991 Gulf War.
Japanese media have reported that the army will have portable anti-tank rocket launchers and recoilless guns to protect against possible suicide bomb attacks.
A special law allowing the dispatch was passed by Japan's parliament in July but only under the condition that the troops be sent to a place away from combat.
Japanese troops have served non-combat roles in UN peacekeeping operations in several countries - including Cambodia, Rwanda, and East Timor.