These tunics were known as "Maternity Tunics" - they actually have hidden buttons which do up diagonally at the side front of the tunic but are hidden under the facing of the Tunic to prevent snagging they also look pretty smart and were favoured by many RFC men http://ourpasthistory.com/Gallery/WW1/Untitled_Scanned_49 1912 was the date for the "maternity jacket" for OR's but the officer's version was only adopted in 1914.
The link in the post above is presumably of an Air Mechanic (equivalent to Private) as he has no badges of rank or "wings". It doesn't show the side fastening very well. The attached picture below, of Andrew Beauchamp-Proctor VC, shows the side fastening a maternity jacket rather better. Come to that, does anyone know the official name for this garment? Surely it wasn't officially called a maternity jacket?
Also referred to as the Plastron Fronted Jackets, and the official Serge Drab Mixture, Royal Flying Corps Issue
In fact, this style was not unique to Britain - most European armies used similar styles for some of their units, especially the cavalry. Here is a photo of Manfred, Freiherr von Richthofen, in a plastron style tunic. He was an Uhlan - a type of German cavalryman before joining the air service, and like all other volunteers for the Luftstreitkrafte he retained the uniform and rank of his original unit.
