The military history of New Zealand during World War II began when New Zealand entered the Second World War by declaring war on Nazi Germany with the United Kingdom in 1939, and expanded to the Pacific War when New Zealand declared war on Imperial Japan following the attack on Pearl Harbor in 1941. New Zealand's forces were soon serving across Europe and beyond, where their reputation was generally very good. In particular, the force of the New Zealanders who were stationed in Northern Africa and Southern Europe was known for its strength and determination, and uniquely so on both sides.

New Zealand provided personnel for service in the Royal Air Force (RAF) and in the Royal Navy and was prepared to have New Zealanders serving under British command. There were many instances of New Zealanders commanding troops on their own, whether their own or a mixture of theirs and foreign ones; notable commanders include Lieutenant-General Bernard Freyberg and Lieutenant-Colonel Fred Baker. Their stationing in North Africa and Greece, specifically during the First and Second Battles of El Alamein and the Freyburg-commanded Crete campaign, was generally well known on either side for its strength, effectiveness and "spiritual" connection. Royal New Zealand Air Force (RNZAF) pilots, many trained in the Empire Air Training Scheme, were sent to Europe but, unlike the other Dominions, New Zealand did not insist on its aircrews serving with RNZAF squadrons, so speeding up the rate at which they entered service. The Long Range Desert Group was formed in North Africa in 1940 with New Zealand and Rhodesian as well as British volunteers, but included no Australians for the same reason.

The New Zealand government placed the New Zealand Division of the Royal Navy at the Admiralty's disposal and made available to the RAF 30 new Wellington medium bombers waiting in the United Kingdom for shipping to New Zealand. The New Zealand Army contributed the 2nd New Zealand Expeditionary Force (2NZEF).

Background Diplomatically, New Zealand had expressed vocal opposition to fascism in Europe and also to the appeasement of fascist dictatorships, and national sentiment for a strong show of force met with general support. Economic and defensive considerations also motivated New Zealand involvement—reliance on Britain meant that threats to Britain became threats to New Zealand too in terms of economic and defensive ties.

There was also a strong sentimental link between the former British colony and the United Kingdom, with many seeing Britain as the "mother country" or "Home". This was reinforced by New Zealand's status as a "white dominion" of the British Empire. The New Zealand Prime Minister of the time Michael Joseph Savage summed this up at the outbreak of war with a broadcast on 5 September (largely written by the Solicitor-General Henry Cornish) that became a popular cry in New Zealand during the war: It is with gratitude in the past, and with confidence in the future, that we range ourselves without fear beside Britain, where she goes, we go! Where she stands, we stand!The Empire and the Second World War Radio 4, episode 88

Declaration of war on Nazi Germany The state of war with Germany was officially held to have existed since 9:30 pm on 3 September 1939 (local time), simultaneous with that of Britain, but in fact New Zealand's declaration of war was not made until confirmation had been received from Britain that their ultimatum to Germany had expired. When Neville Chamberlain broadcast Britain's declaration of war, a group of New Zealand politicians (led by Peter Fraser because Prime Minister Michael Savage was terminally ill) listened to it on the shortwave radio in Carl Berendsen's room in the Parliament Buildings. Because of static on the radio, they were not certain what Chamberlain had said until a coded telegraph message was received later from London. This message did not arrive until just before midnight because the messenger boy with the telegram in London took shelter due to a (false) air raid warning. The Cabinet acted after hearing the Admiralty's notification to the fleet that war had broken out. The next day the Cabinet approved nearly 30 war regulations as laid down in the War Book, and after completing the formalities with the Executive Council the Governor-General, Lord Galway, issued the Proclamation of War, backdated to 9.30 pm on 3 September.

Home front

In total, around 140,000 New Zealand personnel served overseas for the Allied war effort, and an additional 100,000 men were armed for Home Guard duty. At its peak in July 1942, New Zealand had 154,549 men and women under arms (excluding the Home Guard) and by the war's end, a total of 194,000 men and 10,000 women had served in the armed forces at home and overseas.

Auxiliary services were raised for women: the Women's Auxiliary Army Corps was the largest, followed by the Women's Auxiliary Air Force, and then the Women's Royal New Zealand Naval Service.

Conscription was introduced in June 1940, and volunteering for Army service ceased from 22 July 1940, although entry to the Air Force and Navy remained voluntary. Difficulties in filling the Second and Third Echelons for overseas service in 1939–1940, the Allied disasters of May 1940 and public demand led to its introduction. Four members of the cabinet including Prime Minister Peter Fraser had been imprisoned for anti-conscription activities in World War I, the Labour Party was traditionally opposed to it, and some members still demanded "conscription of wealth before men". From January 1942, workers could be "manpowered" or directed to essential industries.

Access to imports was hampered and rationing made doing some things very difficult. Fuel and rubber shortages were overcome with novel approaches. In New Zealand, industry switched from civilian needs to making war materials. New Zealand and Australia supplied the bulk of foodstuffs to American forces in the South Pacific, as Reverse Lend-Lease. With earlier commitments to supply food to Britain this led to both Britain and America (MacArthur) complaining about food going to the other ally (and Britain commenting on the much more generous ration allocations for American soldiers; General George Marshall admitted that the meat ration was too large, but he was not going to challenge the ration set by Congress). By 1943 there was a manpower crisis, and eventually the withdrawal of the Third Division from the Pacific. To alleviate manpower shortages in the agricultural sector, the New Zealand Women's Land Army was created in 1940; a total of 2,711 women served on farms throughout New Zealand during the war.

Axis naval activity in New Zealand waters

German and Japanese surface raiders and submarines operated in New Zealand waters on several occasions in 1940, 1941, 1942, 1943 and 1945, sinking a total of four ships while Japanese reconnaissance aircraft flew over Auckland and Wellington preparing for a projected Japanese invasion of New Zealand.

During the winter of 1944, the government hastened work on docks and repair facilities at Auckland and Wellington following a British request, to supplement the bases and repair yards in Australia needed for the British Pacific Fleet.

Land forces Greek campaign

The New Zealand authorities deployed the 2nd New Zealand Expeditionary Force for combat in three echelons – all originally destined for Egypt, but one diverted to Scotland (it would arrive there in June 1940) following the German invasion of France. In April 1941, after a period training in Egypt, 2NZEF's New Zealand 2nd Division, stationed in Egypt, deployed to take part in the defence of Greece against invasion by Italian troops, and soon German forces too when they joined the invasion. This defence was mounted alongside British and Australian units – the corps-size Commonwealth contingent under the command of British General Henry Maitland Wilson known together as W Force, supported a weakened Greek Army.

As German panzers began a swift advance into Greece on 6 April, the British and Commonwealth troops found themselves being outflanked and were forced into retreat. By 9 April, Greece had been forced to surrender and the 40,000 W Force troops began a withdrawal from the country to Crete and Egypt, the last New Zealand troops leaving by 29 April.

During this brief campaign, the New Zealanders lost 261 men killed, 1,856 captured and 387 wounded.

Crete

Two of the three brigades of the New Zealand 2nd Division had evacuated to Crete from Greece (the third and division headquarters went to Alexandria). New Zealanders bolstered the Crete garrison to a total of 34,000 British and Commonwealth soldiers (25,000 evacuated from Greece) alongside 9,000 Greek troops (see Crete order of battle for more detail). Evacuated to Crete on 28 April (having disregarded an order to leave on 23 April), the New Zealand General Freyberg became commander of the Allied forces on Crete on the 30th. Ultra intercepts of German signals had already alerted Allied commanders to the German plans to invade Crete with Fallschirmjäger (Luftwaffe paratroopers). With this knowledge, General Freyberg began to prepare the island's defences, hampered by a lack of modern and heavy equipment, as the troops from Greece had in most cases had to leave only with their personal weapons. Although German plans had underestimated Greek, British and Commonwealth numbers, and incorrectly presumed that the Cretan population would welcome the invasion, Freyberg was still faced with the harsh prospect that even lightly equipped paratroopers could overwhelm the island's defences.

Operation Mercury opened on 20 May when the German Luftwaffe delivered Fallschirmjäger around the airfield at Maleme and the Chania area, at around 8:15 pm, by paradrop and gliders. Most of the New Zealand forces were deployed around this north-western part of the island and with British and Greek troops they inflicted heavy casualties upon the initial German attacks. Despite near complete defeat for their landing troops east of the airfield and in the Galatas region, the Germans were able to gain a foothold by mid-morning west of Maleme Airfield (5 Brigade's area) – along the Tavronitis riverbed and in the Ayia Valley to the east (10 Brigade's area – dubbed 'Prison Valley').

Maleme

Over the course of the morning, the 600-strong New Zealand 22 Battalion defending Maleme Airfield found its situation rapidly worsening. The battalion had lost telephone contact with the brigade headquarters; the battalion headquarters (in Pirgos) had lost contact with C and D Companies, stationed on the airstrip and along the Tavronitis-side of Hill 107 (see map) respectively and the battalion commander, Lieutenant-Colonel Leslie Andrew (VC) had no idea of the enemy paratrooper strength to his west, as his observation posts lacked wireless sets. While a platoon of C Company situated northwest of the airfield, nearest the sea, was able to repel German attacks along the beach, attacks across the Tavronitis bridge by Fallschirmjäger were able to overwhelm weaker positions and take the Royal Air Force camp. Not knowing whether C and D Companies had been overrun, and with German mortars firing from the riverbed, Colonel Andrew (with unreliable wireless contact) ordered the firing of white and green signals – the designated emergency signal for 23 Battalion (to the south-east of Pirgos), under the command of Colonel Leckie, to counterattack. The signal was not spotted, and further attempts were made to get the message through to no avail. At 5:00 pm, contact was made with Brigadier James Hargest at the New Zealand 2nd Division headquarters, but Hargest responded that 23 Battalion was fighting paratroopers in its own area, an untrue and unverified assertion.