Yes, I did, too!!
It occurs in HMS Heligoland. Here's the text - an excerpt from my book :-
Operation Wagner remains something of a mystery, mainly because of the intense secrecy, the restriction on use of records and the deaths of most of those who planned and executed it. What is clear is that KG 202 (SS) were involved, flying thirty aircraft east to Tomsk for a diving Mistel attack on the entrances and the tunnel housing Stalin's last headquarters. The NKGB assembled reports that it sent to Soviet Consuls in Britain and the USA, these being the main source of historical truth, although media-funded excavations in 2004 did discover more facts and some aircraft wreckage. On 14th April 1944, the Wagner force took off from airfields near Kyubyshev and flew to Tomsk, where they flare-marked the tunnel entrances, attacking with new bombers converted into Mistels. The impacts caved in the tunnel entrances and adits, before the remaining Mistels were used to cave in part of the tunnel's length.
A very nasty feature was that half a dozen of the attackers were used to blast the caps off the two tunnel air vents, then to dump quantities of nerve gas anad mustard gas into the workings. The ones that missed the vents created a zone of persistent contamination that delayed approach and rescue for far too long, so those in the tunnel not killed by cave-ins were to die from gas poisoning or asphyxiation. Figures for deaths from the attack vary from 350 to 4,000 - most of those being amongst rescue crews - and later investigations showed that the contaminated rubble was a serious hazard. Stalin's body was recovered by the miners and was both crushed and contaminated, so it was cremated by the NKGB after Malenkov authorised this.
Stalin’s death was initially considered a blow, but replaceable, until the effects upon the Soviet consciousness became clear; Malenkov and Molotov had none of the charisma Stalin had possessed, nor the fear he had inspired. As Gombos and Hitler had intended, this removal of Stalin led to a collapse of the Soviet system into a network of warlords' fiefs, most of them too fragmented to last. Between the Reich and Pacific Siberia, Western Siberia descended into the kind on anarchy only seen in parts of the pre-1914 Caucasus and Balkans. The fragmentation was made worse by the Luftwaffe destroying bridges and tunnels by free-fall bombs, Hs 293 rocket-powered glide bombs and derivatives of the Fi 103 flying bomb.