Question: How many people in the country that built an experimental 6kV DC railway died in the war?

full_context: Document 1: World War II casualties: World War II was the deadliest military conflict in history in absolute terms of total casualties. Over 60 million people were killed, which was about 3% of the 1940 world population (est. 2.3 billion).
Document 2: Railway electrification system: DC systems (especially third-rail systems) are limited to relatively low voltages and this can limit the size and speed of trains and cannot use low-level platform and also limit the amount of air-conditioning that the trains can provide. This may be a factor favouring overhead wires and high-voltage AC, even for urban usage. In practice, the top speed of trains on third-rail systems is limited to 100 mph (160 km/h) because above that speed reliable contact between the shoe and the rail cannot be maintained.
Document 3: Railway electrification system: Railways must operate at variable speeds. Until the mid 1980s this was only practical with the brush-type DC motor, although such DC can be supplied from an AC catenary via on-board electric power conversion. Since such conversion was not well developed in the late 19th century and early 20th century, most early electrified railways used DC and many still do, particularly rapid transit (subways) and trams. Speed was controlled by connecting the traction motors in various series-parallel combinations, by varying the traction motors' fields, and by inserting and removing starting resistances to limit motor current.
Document 4: Railway electrification system: 1,500 V DC is used in the Netherlands, Japan, Republic Of Indonesia, Hong Kong (parts), Republic of Ireland, Australia (parts), India (around the Mumbai area alone, has been converted to 25 kV AC like the rest of India), France (also using 25 kV 50 Hz AC), New Zealand (Wellington) and the United States (Chicago area on the Metra Electric district and the South Shore Line interurban line). In Slovakia, there are two narrow-gauge lines in the High Tatras (one a cog railway). In Portugal, it is used in the Cascais Line and in Denmark on the suburban S-train system.
Document 5: Railway electrification system: 3 kV DC is used in Belgium, Italy, Spain, Poland, the northern Czech Republic, Slovakia, Slovenia, South Africa, Chile, and former Soviet Union countries (also using 25 kV 50 Hz AC). It was formerly used by the Milwaukee Road from Harlowton, Montana to Seattle-Tacoma, across the Continental Divide and including extensive branch and loop lines in Montana, and by the Delaware, Lackawanna & Western Railroad (now New Jersey Transit, converted to 25 kV AC) in the United States, and the Kolkata suburban railway (Bardhaman Main Line) in India, before it was converted to 25 kV 50 Hz AC.
Document 6: Soviet Union: The Soviet Union suffered greatly in the war, losing around 27 million people. Approximately 2.8 million Soviet POWs died of starvation, mistreatment, or executions in just eight months of 1941 -- 42. During the war, the Soviet Union together with the United States, the United Kingdom and China were considered as the Big Four of Allied powers in World War II and later became the Four Policemen which was the foundation of the United Nations Security Council. It emerged as a superpower in the post-war period. Once denied diplomatic recognition by the Western world, the Soviet Union had official relations with practically every nation by the late 1940s. A member of the United Nations at its foundation in 1945, the Soviet Union became one of the five permanent members of the United Nations Security Council, which gave it the right to veto any of its resolutions.
Document 7: World War I casualties: The total number of military and civilian casualties in World War I was about 40 million: estimates range from 15 to 19 million deaths and about 23 million wounded military personnel, ranking it among the deadliest conflicts in human history.
Document 8: Railway electrification system: Most electrification systems use overhead wires, but third rail is an option up to about 1,200 V. Third rail systems exclusively use DC distribution. The use of AC is not feasible because the dimensions of a third rail are physically very large compared with the skin depth that the alternating current penetrates to (0.3 millimetres or 0.012 inches) in a steel rail). This effect makes the resistance per unit length unacceptably high compared with the use of DC. Third rail is more compact than overhead wires and can be used in smaller-diameter tunnels, an important factor for subway systems.
Document 9: World War II casualties: World War II was the deadliest military conflict in history in absolute terms of total casualties. Over 60 million people were killed, which was about 3% of the 1940 world population (est. 2.3 billion). The tables below give a detailed country - by - country count of human losses. World War II fatality statistics vary, with estimates of total deaths ranging from 50 million to more than 80 million. The higher figure of over 80 million includes deaths from war - related disease and famine. Civilians killed totalled 50 to 55 million, including 19 to 28 million from war - related disease and famine. Military deaths from all causes totalled 21 to 25 million, including deaths in captivity of about 5 million prisoners of war.
Document 10: World War I casualties: The total number of military and civilian casualties in World War I was more than 41 million: there were over 18 million deaths and 23 million wounded, ranking it among the deadliest conflicts in human history.
Document 11: Railway electrification system: There has, however, been interest among railroad operators in returning to DC use at higher voltages than previously used. At the same voltage, DC often has less loss than AC, and for this reason high-voltage direct current is already used on some bulk power transmission lines. DC avoids the electromagnetic radiation inherent with AC, and on a railway this also reduces interference with signalling and communications and mitigates hypothetical EMF risks. DC also avoids the power factor problems of AC. Of particular interest to railroading is that DC can supply constant power with a single ungrounded wire. Constant power with AC requires three-phase transmission with at least two ungrounded wires. Another important consideration is that mains-frequency 3-phase AC must be carefully planned to avoid unbalanced phase loads. Parts of the system are supplied from different phases on the assumption that the total loads of the 3 phases will even out. At the phase break points between regions supplied from different phases, long insulated supply breaks are required to avoid them being shorted by rolling stock using more than one pantograph at a time. A few railroads have tried 3-phase but its substantial complexity has made single-phase standard practice despite the interruption in power flow that occurs twice every cycle. An experimental 6 kV DC railway was built in the Soviet Union.
Document 12: Railway electrification system: In the Soviet Union, in the 1970s, a comparison was made between systems electrified at 3 kV DC and 25 kV AC (50 Hz). The results showed that percentage losses in the overhead wires (catenary and contact wires) was over 3 times greater for 3 kV DC than for 25 kV AC. But when the conversion losses were all taken into account and added to overhead wire losses (including cooling blower energy) the 25 kV AC lost a somewhat higher percent of energy than for 3 kV DC. Thus in spite of the much higher losses in the catenary, the 3 kV DC was a little more energy efficient than AC in providing energy from the USSR power grid to the terminals of the traction motors (all DC at that time). While both systems use energy in converting higher voltage AC from the USSR's power grid to lower voltage DC, the conversions for the DC system all took place (at higher efficiency) in the railway substation, while most of the conversion for the AC system took place inside the locomotive (at lower efficiency). Consider also that it takes energy to constantly move this mobile conversion hardware over the rails while the stationary hardware in the railway substation doesn't incur this energy cost. For more details see: Wiki: Soviet Union DC vs. AC.
Document 13: Modern history: It is possible that around 62 million people died in the war; estimates vary greatly. About 60% of all casualties were civilians, who died as a result of disease, starvation, genocide (in particular, the Holocaust), and aerial bombing. The former Soviet Union and China suffered the most casualties. Estimates place deaths in the Soviet Union at around 23 million, while China suffered about 10 million. No country lost a greater portion of its population than Poland: approximately 5.6 million, or 16%, of its pre-war population of 34.8 million died.
Document 14: World War II: World War II (often abbreviated to WWII or WW2), also known as the Second World War, was a global war that lasted from 1939 to 1945, although conflicts reflecting the ideological clash between what would become the Allied and Axis blocs began earlier. The vast majority of the world's countries -- including all of the great powers -- eventually formed two opposing military alliances: the Allies and the Axis. It was the most global war in history; it directly involved more than 100 million people from over 30 countries. In a state of total war, the major participants threw their entire economic, industrial, and scientific capabilities behind the war effort, blurring the distinction between civilian and military resources. World War II was the deadliest conflict in human history, marked by 50 to 85 million fatalities, most of which were civilians in the Soviet Union and China. It included massacres, the genocide of the Holocaust, strategic bombing, premeditated death from starvation and disease and the only use of nuclear weapons in war.
Document 15: Slavs: During World War II, Hitler's Generalplan Ost (general plan for the East) entailed killing, deporting, or enslaving the Slavic and Jewish population of occupied Eastern Europe to create Lebensraum (living space) for German settlers. The Nazi Hunger Plan and Generalplan Ost would have led to the starvation of 80 million people in the Soviet Union. These partially fulfilled plans resulted in the deaths of an estimated 19.3 million civilians and prisoners of war.
ground_truth: 23 million
sub_queries: Where was an experimental 6kV DC railway built? Answer: the Soviet Union
How many deaths did the Soviet Union suffer in the war? Answer: 23 million