13. Defensor Capitoli - Building up the air defense for Helsinki
13.1. Guns, guns, guns
The main focus of anti-aircraft effort in 1932-1936 was the build-up of anti-aircraft defense for Helsinki and Viipuri. Helsinki as the capital city, most important population and industrial center, was the natural focus of the defense effort. Viipuri was the second largest city and also major logistical center for Army of the Isthmus in wartime.
In defensive tasks Helsinki was the only one designated with priority number I, Viipuri the only one with priority number II. Turku, Kouvola and Riihimäki were with priority number III, Tampere, Jyväskylä and Oulu with priority number IV.
The new organization for defending Helsinki was called
Helsingin Ilmatorjuntarykmentti (Helsinki AA regiment).
As reference when developing air defense for Helsinki the defense of Paris and London were used as for comparison. In the end, air defense of Paris with it's better command and control facilities and simpler layout between fighter and anti-aircraft defense zones was used as inspiration. In French model of anti-aircraft defense the idea was that commander of the anti-aircraft battalion would decide the target for the battalion which would shoot the target with at least two batteries. First shot would be with time on target to ensure maximum effect. To ensure this a good command and control network would be essential together with automatic fuze setting machinery. During night, unless target was spotted with lead searchlight, only barrage firing would be possible.
Mikkola was very optimistic with the ballistic capabilities of 105mm anti-aircraft gun, assuming 8000 meters range for firing which in practice proved to be too far. In hindsight, he also did not create a schwerpunkt but wanted to ensure good all-round capability. This meant that theoretically the four fixed batteries were deployed in a diamond formation, with 8000 meters distance between each battery and distance of 5500 meters from the protected point, Helsinki railway station. Thus the fixed batteries were deployed Santahamina, Viikki, Haaga and Lauttasaari.
Each super-heavy battery had two twin turrets situated 300 meters apart with a fire control station in the middle. For close-in defense four twin 7,62mm AAMG's were provided.
A battery cost some 20 million marks, which was a very large sum. In the end, only Helsinki got fixed superheavy batteries for a total of 80 million marks. Each battery was akin of something like warship on the rocks and received names like warship. (Kullervo,
Theoretically it was estimated than when counting the shell weight and area to be covered the four super heavy batteries would be equivalent of 36 four gun 76mm batteries, or 108 pieces, and this was not even counting the height which could be achieved. As for price, 108 modern 76mm pieces alone (1,2 million marks each) would have cost some 130 million marks and 36 predictors with reserve equipment (2 million marks each) some 72 million, for a total of 200 million marks.
A battery cost some 20 million marks, which was a very large sum. In the end, only Helsinki got fixed superheavy batteries for a total of 80 million marks. Each battery was akin of something like warship on the rocks and received names like warship (Aino, Kyllikki, Marjatta, Tellervo).
13.2. Detection, command and control
For detecting the enemy air attack the earliest warning would be provided by radio intercepts. This would be followed by acoustic location equipment, large scale sound mirrors of British style were constructed in some of the islands close to Helsinki. Aerial observation posts were from 1936 onwards connected through filtering centers (IPAK) to national air command center
(Pääjohtokeskus) located in Ilmala, Helsinki, with callsign Akropoli. National air command center had direct line to YLE radio broadcasting center which could give air raid warnings through radio broadcast with coded map.
With increasing speed of aircraft from 1938 onwards the data of aerial targets was transferred electronically from plotting boards of filtering centers to national air command center.
Aerial observation posts were planned to be installed on ice on Gulf of Finland during winter, and during summertime use of picket boats was planned.
After batteries were alerted they could spot the target by visual means or try to get target data from searchlights during night. Searchlight units had acoustic locators whose information was used in order to try to find target with larger (150-210cm diameter) searchlights. After target was located, it was followed by smaller lead searchlights (90-110cm diameter). Lead searchlights transferred the bearing and azimuth data to batteries and battalion command posts automatically, so they could in principle form a target plot with two or more searchlights. In practice, this data was used to help predictor to find a target.
Predictor was aimed visually to target selected by battery commander. The predictors range and bearing information was transferred electronically to the superheavy battalion command post in which battalion commander could, if he wanted, direct the whole engagement with the target. Time on target was constantly calculated to ensure that 8 first shells would detonate simultaneously on target. The whole process was something more akin to artillery use of a warship than that of an antiaircraft unit and owed much to French ideas.
105mm guns had mechanical time fuzes which were automatically set by fuze setting device (turned to correct position) to ensure rapid and accurate firing.
The whole arrangement was incredibly ambitious and indeed, while the building was finished in 1935 it was only in 1938 that everything worked properly.
Primitive command plot used in 1920's and later on with divisional anti-aircraft battalions
Battalion command post, auxiliary plotting table
On left and right, time fuzes of German 88mm AA-gun. Notice the setting ring on both.
The whole anti-aircraft machinery demanded an incredible amoung of precision engineering, demanding much care.
(Note: I'm assuming the money saved from not purchasing Vickers guns and their assorted equipment, roughly 20 million marks, will go to improving signals and command equipment.)
