[Alex Smart]

Hello Mirek,
The following is taken from an early issue of an Air Enthusiast bi-monthly magazine.

"7 April, the 1st Regiment was fully committed - in company with the 3rd and 7th - to attack the most threatening of the German columns advancing from the Bulgarian frontier towards Skoplje. Ordered to attack armoured vehicles between Krive Palanka and Stracin, the Blenheims operated in three-aircraft elements, at intervals of 30 minutes. Some hits were observed, but heavy flak and small arms fire took their toll; the aircraft flown by the CO of the 204. eskadrila was destroyed and three others made forced landings, so that only 18 Blenheims remained available for further operations by the 1st Regiment.
Much worse befell the 8th Regiment on this day. Based too far away from the Bulgarian frontier to join with the other bomber units, its Blenheims were again directed to operate over South Austria. In very poor weather, only one or two of the bombers found suitable targets, the others returning to Rovine with their bombs intact; one Blenheim made an emergency landing near Graz. Later in the day, 12 Blenheims set out again to strike at Railroad junctions and Military installations in the region of the Hungarian towns of Pecz and Szeged. Again lacking fighter protection, six of the Blenheims were shot down by Bf109E's of II/JG54, two more being destroyed as they landed and three being seriously damaged. The CO's of both Grupa and of both Eskadrila of the 68th Grupa were among those killed, one of the commanders succeeding in shooting down a BF109 shortly before his Blenheim crashed. After this massacre, the 8th bomber regiment was virtually out of action for the remainder of the conflict, although a few more sorties were flown on 8th April without further loss.
On 8th April eight Blenheims of 62 Grupa set out from Bijelina to attack German armour, as on the previous day, but only one three-aircraft element found the target in the Kacanik gorge, in extremely unfavourable weather with low clouds, rain and snow. Making a low-level attack in single file on the Panzer column, the first and third Blenheims were shot down, costing the life of the commander of the 1st Bomber Regiment, Pukovnik (Colonel) Ferdo Gradisnik - the only JKRV officer of this rank to lose his life during the April war. Another Blenheim from this mission was lost in an emergency landing at its home base. Better results were obtained by the 10 Blenheims of 61 Grupa which attacked the same target later that day from higher altitude, achieving hits and returning without loss. Five aircraft of 11 Grupa attacked targets in the same area losing one Blenheim to flak and a Hind that crashed in bad weather during the return to Veliki Radinci."

I know this only deals with Yugoslav Blenheims and not other bombers ( 60 or so Do17's and 26 or so S79's ) of the Yugoslav A/F but I hope this is of some help to you.
For a more comprehensive account I suggest you try to get a copy of Grub Streets "Air War for Yugoslavia Greece and Crete" by Shores , Cull and Malizia.
Alex