The Ki-45 was Japan's answer to the heavy fighter like Germany's Bf-110. However, it was not used as a bomber escort, but mainly for ground attack, a role in which it was relatively successful. It was also used as a bomber interceptor and was armed with Schräge Muzik or obliquely mounted cannon in the aft cockpit. 

The Ki-45 had an extremely long gestation period before it finally entered production. There were all sorts of problems much of them relating to tail flutter and lack of general stability. There was also a lack of power from the chosen engines. As this aircraft was also being developed concurrently with the Ki-48 and using many of the same components, similar problems cropped up with the Ki-48. Eventually the airframe was modified and more powerful engines used bring the aircraft up to specifications.

Most of the Ki-45s that entered service were the Ki-45KAI (KAI = modified) version. There were four subtypes of the Ki-45KAI; the a, b, c, and d versions. They are all differentiated by armament and nose shapes.  

As for some specs, the top speed was 340 mph, range about 1,400 miles and a little over 1,700 aircraft were built. One was experimentally fitted with a 75mm cannon, but it proved too much for the light airframe of the Ki-45.

The aircraft was relatively outclassed by most modern Allied planes, but in some of the areas 'least travelled' by the Allies, such as Manchuria and Indo-China, it was still quite effective. Manchukuo (満州国, lit. "State of Manchuria") was a puppet state in Manchuria and eastern Inner Mongolia created by former Qing Dynasty officials with help from Imperial Japan in 1932. The state was founded and administered by Imperial Japan, with Puyi, the last Qing emperor, as the nominal regent and emperor. Manchukuo's government was abolished in 1945 after the defeat of Imperial Japan at the end of World War II.

The Manchukuo Imperial Air Force (大満州帝国空軍, Dai Manshū Teikoku Kūgun) was established in February 1937, initially with 30 men selected from the Manchukuo Imperial Army and trained at the Japanese Kwantung Army aircraft arsenal in Harbin. The official air force's predecessor was the Manchukuo Air Transport Company (later re-named the Manchukuo National Airways) a paramilitary airline formed in 1931, which undertook transport and reconnaissance missions for the Japanese military.

The first air unit of the Manchukuo Air Force was established at the airfield in Xinjing, under the command of 1st Lieutenant Uta, and initially had only one aircraft: a French-built Nieuport-Delage Ni-D29 biplane. Kawasaki Type 88 (KDA-2) light bombers and Nakajima Type 91 fighters were later supplied from Japan.

A second air unit was established in Fengtien and the third air unit in Harbin from 1938-1939. In July 1940, an Air Defense HQ was created in Xinjing.

Initially, only Japanese pilots and ground crews were also deployed. After 1940, the Japanese allowed native ethnic Manchus to receive pilot training. On 30 August 1940, a flight school was established in Fengtien to teach both military and civil pilots. The training program received a severe setback in January 1941 when approximately 100 pilot cadets rebelled, and fled to join to anti-Japanese guerillas after killing their instructors. During September to October 1942 the school received more than twenty training aircraft, including Tachikawa Ki-9 "Spruce", Tachikawa Ki-55 "Ida" and Mansyū Ki-79 advanced trainers

In addition, a transport section with three Nakajima Ki-34 passenger aircraft was established to serve the needs of the imperial court. Additional Junkers Ju-86Z-2, Tachikawa Ki-54 "Hickory" and Mansyu "Hayabusa III" provided for government transportation needs.

From 1944, the Manchukuo Imperial Air Force came under the command of the Japanese 2nd Air Army. At that point, it had around 100 to 120 combat aircraft.

From 1941 to the end of World War II, the main equipment of the Manchukuo Air Force was the Nakajima Ki-27b "Nate" light fighter. Money to pay for these fighters was “donated” by various Japanese companies based in Manchukuo. Primarily a fighter force, the only tactical bomber in Manchukuo service during World War II was the Kawasaki Ki-32.

The Manchukuo Air Force requested Type 1 Nakajima Ki-43 IIa Hayabusa "Oscar" and Type 2 Nakajima Ki-44 IIb Shoki "Tojo" fighter/interceptors from Japan in early 1945. However, these more advanced aircraft were supplied in only small numbers. (Apparently some Ki-45s were also supplied. Ed)

As American air raids against Manchukuo increased in frequency towards the end of the war, the Manchukuo Air Force resorted to kamikaze tactics, with the first successful ramming attack (by a Ki-27) on a USAAF B-29 Superfortress strategic bomber occurring in December 1944. The Manchukuo Air Force also suffered from a chronic shortage of fuel, as Japanese military aviation had first claim to supplies.

In 1945, the American air raids against Manchuria decreased and the threat of the Soviet invasion increased. The Manchukuo Air Force changed its training from interception to emphasize ground attack against armored vehicles. During Operation August Storm, when the Soviet Union invaded Manchukuo, the Japanese 2nd Air Army ordered the Manchukuo Air Force to train for suicide attacks against Soviet tanks. However, the war ended before attack plans could be executed.