I first wrote a book on the Belfast Blitz in 1989 - partly because of my deep affection for the city and also because virtually no research had been conducted into it. I was conscious then that there were many sources I should have looked at and always felt that, at some point, I would attempt to write a more definitive account.
I began this in 2010. I interviewed numerous people and consulted a wealth of published material. But my main new source was the wealth of documentary material drawn from almost 30 archive centres.
This included: at the Public Record Office of Northern Ireland, the papers of Belfast City Council; at the Linen Hall Library, civil defence message books for 'D district' covering April/May 1941 - ie the actual messages sent by wardens to their local HQ during the raids, in the area of north Belfast which was the most severely bombed of any in the city; in Dublin, reports by Eire's lookout posts, meteorological records and Government files relating to key aspects of the Blitz; and in London, the papers of servicemen who served locally in 1941, Luftwaffe target folders compiled to brief the crews later designated to bomb Belfast and the war diaries for those military units who manned its AA guns, fighter aircraft and searchlights.
The book, Belfast Blitz: The City In The War Years, examines the reasons why Belfast was ill-prepared for the Blitz. It had too few shelters and anti-aircraft guns, fighter aircraft only equipped for daytime operations, no searchlights and few people had been evacuated.
In part, this was because the city was thought to be too insignificant and remote from Germany to merit elaborate preparations. Its long immunity from attack encouraged the hope that it might escape altogether and there was a feeling that Hitler might respect Irish neutrality and, so, not bomb it.
Blame is often attributed to the incompetence of the Stormont Government. But anti-aircraft guns and searchlights were in short supply throughout the UK, not just in Northern Ireland. Also, the key decisions about how the available supplies should be allocated were made in London, not in Belfast.
From mid-1940 there was a growing expectation amongst politicians and officials that Belfast would be attacked. This was because of the city's increasing importance as a munitions and military centre.
The fall of France in June 1940 increased its vulnerability. After this, Germany had air bases in northern France. Also, the Admiralty diverted shipping from Britain's vulnerable southern ports to those in the north west - Glasgow, Liverpool, Bristol and Belfast.
Concern was increased by the pattern of the Blitz on Britain by early 1941. It was increasingly directed at these western ports; there were mounting fears that Belfast would be next.
Furthermore, there was evidence that Luftwaffe activity over the city was increasing - laying mines in Belfast Lough almost daily by July 1940 and reports of reconnaissance aircraft overhead.
The book describes the raids in detail and their impact. The first was the Dockside raid (April 7/8, 1941), when 13 people died, 12 in the docks area. Though popularly referred to as the "wee" raid, 500 bombers attacked the UK that night; there were at most eight over Belfast at any one time.
It seemed certain that the Luftwaffe would return and, in preparation, a smokescreen was set up to obscure the docks and searchlight units arrived on April 10.
Belfast's second raid, on Easter Tuesday night (April 15/16) is the one most deeply embedded in the popular memory. Some 180 bombers participated and dropped 200 tons of high explosives and 30,000 incendiaries.
The most striking feature of the raid was that the docks sustained little damage. Instead, it was the working-class terraces to the north of the city which suffered most (for example, the chronicle for St Patrick's Church, Donegall Street, records that 130 of its parishioners died).
The explanation most commonly offered was that the Luftwaffe mistook Belfast's Waterworks for the docks and bombed the district surrounding it. It is understandable how the bombers might have missed the harbour area. Weather conditions were poor; one-third of the bombers designated to attack the city failed to reach it and diverted to targets in Britain.
Military reports also stressed the effectiveness of the smokescreen in obscuring the harbour area. Bombing techniques were primitive; in spite of these conditions, Luftwaffe crews attempted to drop their bombs "by sight".
Their reports on the raid are revealing. They described it as "unsatisfactory", "abortive", predicted that its effect would be "minimal" and results "mediocre". Basically, they did not know what they had struck.
Few claimed to have hit their primary targets in the docks; most knew they had missed them. Other areas were hit - in Londonderry, Newtownards and Bangor. In Belfast, 740 civilians lost their lives.
The death rate was high, because so many bombs fell on densely populated areas, there were few shelters, the fact so few had been evacuated from the city and its defences were inadequate.
Again, it was likely that the Luftwaffe would return; crews knew they had missed their targets. Meanwhile, little could be done to improve the city's defences. "Dangerous" animals in Bellevue Zoo were put down and the number of anti-aircraft guns increased from 22 to 28.
Belfast's second major attack took place on May 4/5. It was shorter, more intense and more accurate than on Easter Tuesday - the Luftwaffe struck its primary targets (the shipyards and aircraft factory). Over almost three hours, 200 bombers dropped 240 tons of high explosives and 100,000 incendiaries.
More than 200 fires were ablaze when the raid ended. It was popularly referred to as the "fire raid". There were fewer casualties; 192 civilians were killed, primarily because it was the docks and city centre area which suffered most.
There were few people about - it was a Sunday night, many workers had refused to work night shifts after Easter Tuesday and 100,000 people had evacuated following that attack.
Possibly the shelters were used more; certainly, the anti-aircraft guns were more active, supplemented this time by HMS Furious.
After this raid Luftwaffe crews expressed elation. Virtually all reported that they had hit their targets, and some claimed that the city's fires were visible from the coasts of Wales and Lancashire.
Belfast's last raid took place on the following night (May 5/6). While 460 bombers attacked UK targets, fortunately just three struck Belfast. It was vulnerable at the time; the water was off over three-quarters of the city and civil defence workers were exhausted.
The bombing of Dublin (May 30/31) was the last occasion when a significant number of bombs were dropped on Ireland. Its causes have prompted speculation. Did the Luftwaffe bomb it by mistake, because the British "bent" their navigation guidance beams, or their aircraft were blown across from Britain by strong easterly winds?
Or was the bombing a calculated act of German retaliation for Eire's breaches of neutrality - most recently evidenced by the help it had given Belfast after air raids there?
In support of the latter is the fact that, prior to the Easter Tuesday raid, Luftwaffe pilots had been given strict instructions to ensure that they did not bomb neutral Ireland.
The book also evaluates in detail the impact of the Blitz - its demographic, social, economic and political consequences; whether it affected Stormont/Westminster relations, or improved those between Northern and southern Ireland, or between the two communities within Northern Ireland (it examines the wartime activities of the IRA).
The air raids caused 960 civilian deaths in Northern Ireland (the book contains the names of almost 900 of them). When military deaths are included, the total rises to more than 1,000.
The Belfast air raids have been described as the "most disastrous event in (its)... history" and they were traumatic and unprecedented. Two of them were particularly heavy.
Thus, half of the city's housing stock was destroyed or damaged, and half of its elementary schools. In May 1941 officials estimated that 220,000 people had evacuated from the city (one-half its population), while tens of thousands "ditched".
Yet the Blitz is still not adequately commemorated; there is no civic memorial to its victims. Hopefully, this omission will be corrected next year - its 75th anniversary.
Brian Barton's Belfast Blitz: The City In The War Years is published by the Ulster Historical Foundation (£19.99)