At the start of the Sino-Japanese war, Tan Won served in the 21st PS, 4th PG. This unit was at the time equipped with Curtiss Hawk IIIs.

On 14 August 1937, the IJNAF Kanoya Kokutai dispatched nine Mitsubishi G3M1 Model 11 long-range bombers under the command of Lieutenant Commander Nitta to attack the Schien Chiao Airfield near Hangchou and nine under the command of Lieutenant Commander Asano to attack the Kwang-teh Airfield. The Japanese planes took off from Matsuyama Airfield in Taipei at 14:50 (local Japanese time), each carrying two 250kg bombs.
The raid was soon spotted by the Chinese and the Chinese intelligence reported that a number of Japanese bombers had taken-off from an airfield Taiwan, crossed the Formosa Strait and were heading north over Chekiang in the direction of Hangchou. At this time, Hangchou was only defended by a handful of Hawk IIIs flown by instructors from the Central Chinese Aviation Academy since reinforcements from Chou Chia-Kou hadn't been able to fly in due to bad weather. Colonel Kao Chi-Hang had previously flown from Nanchang to Schien Chiao to await the 4th PG’s Hawk III’s, which were flying in from Chou Chia-Kou in the Honan Province and which was under his command. The three squadrons of the 4th PG encountered heavy weather en route, with heavy rain and low visibility.
However barely had the warning been received when a number of Hawk IIIs from the 21st and 23rd Squadrons of the 4th PG landed. The newly arrived fighters were hurriedly re-fuelled, but this was far from complete when the air alarm started due to the arrival of Lieutenant Commander Nitta’s bombers. Colonel Kao rushed to his aircraft no. IV-1, which had just been landed by Captain Mao Ying-Chu. Ordering Mao to go get another aircraft, Kao jumped into IV-1 and, without waiting to be refuelled, took off immediately. He joined up with Lieutenant Tan Won who had just spotted Nitta’s flight (1st Shotai) of three G3Ms.
It's possible that they only saw one G3M since according to Japanese records, Nitta’s flight (1st Shotai) did not find Schien Chiao Airfield in their first effort. When they turned back south, the No.3 separated from the flight and Nitta and No.2 missed the airfield again. The latter two could do nothing but flew home. They did not see Chinese aircraft either. The Japanese bomber came in at the low “attack” altitude of 500m, which made it easier for the Chinese to intercept it right after the take-off. The No.3 G3M dropped its bombs on the airfield doing little damage. Tan opened fire on G3M. However, the much more experienced Kao noted that Tan had opened fire from out of effective range. Kao then bore in himself and closed in also on the No.3 Japanese aircraft. He first silenced the two Japanese gunners and then closed in to 20m(!) firing steadily at the left engine. The wing tanks on the left wing caught fire and the G3M crashed burning near the town of Ban Shan near the airfield.
Kao then spotted the 3rd Shotai and attacked the No.2 aircraft between Schien Chiao and Chien Tang River. Again, Kao bore in to close range firing at the fuselage and the left wing on the G3M, putting the left engine out of action. Kao’s engine was then hit by return fire forcing him to return to Schien Chiao.
While Kao was attacking the No.2 plane in the 3rd Shotai, 21st PS Squadron Leader Captain Lee Kuei-Tan and his wingmen Lieutenant Wang Wen-Hua and Lieutenant Liu Chi-Sheng caught up with the No. 3 plane of the same Shotai. Shooting at the hapless G3M repeatedly, the three brought it down near Ban Shan. This G3M (No.3 from 3rd Shotai) had got separated from the rest of the Shotai long before arriving over Shien Chiao.
The 3rd Shotai reported that No.1 and No.2 made their first pass over Schien Chiao from the west. Due to the bad weather they did not drop the bombs in this pass. Instead, they turned back and made the second pass from the east. After finally dropping their bombs, they turned south and sped away, across Chien Tang River. No.2 got its left engine damaged over Shien Chiao (probably by Kao) and was attacked again by three Chinese fighters at 30 nautical miles and 170 deg off Shien Chiao.
The 22nd PS refuelled at Kwang-teh and took off at 16:20 to fly to Schien Chiao where they landed at around 17:00. The 22nd PS was on the ground, refuelling at Schien Chiao when the Japanese bombers dropped their bombs and they scrambled trying to catch the Japanese bombers that were flying east. They flew to the mouth of the Chien Tang Chiang (river) amid low cloud and bad weather where they lost sight of the Japanese aircraft and returned to base. Pilots included in this chase were flight leader Lieutenant Le Yi-Chin and 2nd Lieutenant Chang Kwang-Ming. However, Lieutenant Cheng Hsiao-Yu of the 22nd PS managed to intercept them. Cheng had taken off too late to intercept Nitta’s flights during the attack and flew on to Chien Tang Chiang on a hunch. After passing Weng Chiao Pu Airfield, Cheng reported good visibility below the clouds. Spotting the G3Ms, Cheng gave chase and attacked one of them. Cheng reported shooting at and hitting the right wing of his target. A fire broke out but then quickly went out again. Cheng attacked 6 - 7 times before breaking off when his ammo was exhausted. He reported that it went down at the estuary of Chien Tang River.
It seems that he also had attacked the 3rd Shotai, which reported bombing Schien Chiao 18:20-18:25 Japanese time (17:20-17:25 Chinese time). They reported that they were attacked two different Chinese fighters. The first time was between Schien Chiao Airfield and Chien Tang River (Kao). The second time was approximately 15 minutes after the first attack when the Japanese plane had crossed the Chien Tang River (Cheng). The No.2 plane of the 3rd Shotai was at the receiving end this time as well and managed to limp back to Matsuyama Airfield in Taipei on one engine and made a forced landing. However, as it touched down, the left landing gear collapsed, and the aircraft suffered “moderate damage”. The bomber had suffered 38 hits in the plane's fuselage and tail, 14 hits in the left wing with the left engine put out of action and 21 hits in the right wing. The Japanese later took this plane out of service to be displayed in Japan and, to all intents and purposes, it was written off.
Lieutenant Commander Asano’s Kwang-teh Attack group, took off from Matsuyama at 14:55 Japanese time (13:55 Chinese time) and got lost shortly after reaching the Chekiang coast at 16:45 Japanese time (15:45 Chinese time) due to a typhoon in the Shanghai area, which made the weather terrible. They headed west to try and find a landmark, reaching Chu Chiang River at 17:00. They then turned north to try and find another landmark. At 17:14, Lieutenant Commander Asano gave up and headed south-east back to the Chekiang coast. At 17:45, they reached the town of Ta Ching near Wenchow on the Chekiang coast. They were then able to plot a course to Kwang-teh using two large lakes, Tai Hu and Nan Hu, as waypoints. At 19:30, the Kwang-teh Attack group reported being attacked by a Chinese Hawk III just short of their target. At 19:40, the group dropped 16 250kg bombs on Kwang-teh airfield. Three G3M from this group were hit in the attack. The No.2 plane of the 1st Shotai was hit once. The No.3 plane of the 5th Shotai was hit twice in the left wing and three times in the right. The No.2 plane in 2nd Shotai was hit in a wing tank and was losing fuel with the crew apparently not realizing the extent of the fuel leak at the time. This G3M eventually ran out of fuel just short of the Taiwan coast and ditched just off the lighthouse at the mouth of Keelung Harbour. The ditching could have been avoided had the crew realized the extent of the fuel leak. The 2nd Shotai had not dropped all of its bombs during the attack on Kwang-teh. They decided to bomb Schien Chiao on the way home. At 20:50, they dropped their remaining bombs on Schien Chiao. However, the No.3 G3M from the Shotai became separated from the other two in the gathering darkness. The leader of the 2nd Shotai, Lieutenant Umebayashi, led his two bombers in a 40 minutes search where the No.3 eventually was found and the 2nd Shotai headed back to Taiwan together. At 22:53, the No.2 bomber ran out of fuel and ditched!
The group led by Lieutenant Commander Asano had run into a single Hawk III flown by Captain Chow Ting-Fong (Squadron Leader of the 34th Provisional Pursuit Squadron made up of cadets flying Hawk IIs). Chow was a flight instructor from the Air Force Academy and he reported intercepting a group of Japanese twin engine bombers after flying alone to Kwang-teh at around 18:30. Chow made four firing passes on the nine Japanese bombers from different directions. The first pass was head-on, followed by a climb and diving attack from the front. Pulling up after this pass, Chow attacked from the rear and below. Finally, Chow attacked from the front and below. The Japanese formation consisted of Asano’s leading 1st Shotai with the 2nd Shotai to the left and the 5th Shotai to the right. It is now apparent that Chow attacked each of the Shotais in turn during his firing passes. According to the Japanese reports, one bomber from each Shotai was hit. Since the Kwang-teh attack group did not report being attacked by other Chinese fighters, credit for the No.2 plane of the 2nd Shotai lost in the Keelung Harbour ditching should go to Chow.
The Chinese lost one Hawk III which ran out of fuel when it tried to take off as Nitta's G3Ms arrived overhead. This unfortunate Hawk no. 2105 crashed into a tree, mortally injuring its pilot Lieutenant Liu Shu-Fan. Another pilot from the same flight, Lieutenant Chin An-Yi, was slightly injured when his Hawk no. 2106 also ran out of fuel and ended up force landing next to an AA gun position.
So, the final tally for the day was 3 G3Ms destroyed and one written off on landing. Actually, Chinese pilots made only 3 claims, but AA gun crews also made 3 additional claims. As a result, 6 claims were submitted in total (and publicized for propaganda purposes).

During the night of 14 and 15 August the pilots of the 4th PG at Schien-Chiao airbase had to prepare their fighters themselves since the ground personnel had left the field to take shelter during the air raid on 14 August and had not returned. The pilots carried cans of fuel on their backs from the storage building to the field, punched holes on the cans and fuelled the aircraft themselves. They had not eaten since noon, and were not able to go to bed until 1:30 a.m. They did not sleep long because alarm sounded less than two hours later.
In the early morning on 15 August Colonel Kao Chi-Hang led 21 Hawk III's from the 4th PG to intercept a dawn attack on Hangchow by twelve Type 89 torpedo bombers from the Japanese carrier Kaga. In the confused action in and out of clouds, the 4th PG made 17 claims, more than the total number of Japanese planes in the action. The actual losses were six shot down and two ditched in Hangchow Bay.
Kao quickly shot down one of the Type 89's on the edge of the formation and then attacked another setting it alight. A lucky shot from the starboard quarter hit Kao in the right arm before passing through the instrument panel and damaging the engine in his Hawk No. IV-1. He was forced to land at Schien-Chiao and was out of action for 2 months.
21st PS's Squadron Leader Captain Lee Kuei-Tan in No. 2101 attacked the No. 2 Shotai, shooting down the No. 2 plane over Chao-Er. Two out of the crew of three were seen to bail out but they were over the Chao-er River and probably did not survive. Lee then teamed up with Lieutenant Cheng Hsiao-Yu of 22nd PS in No. 2202 to claim another Type 89. Return fire from the tightly packed Japanese formation was heavy and Lee's No. 2101 received slight damage to its upper wings while Cheng’s No. 2202 took a shot in one of its landing wheels. Cheng’s wingman, 2nd Lieutenant Chang Kuang-Ming also claimed a victory in this combat when he attacked the leader of a group of Japanese bombers. He opened fire with his two machine guns. Tracers and bullets truck his target, and the enemy plane turned into a fireball and plunged out of the sky. He broke off immediately and turned around for another strike.
Lieutenant Huang Yan-Po in No. 2107 attacked the first Shotai, claiming to have shot down the No. 3 aircraft in flames. He too took a shot in the landing wheel. Lieutenant Tan Won in No. 2104 also attacked the same Shotai and claimed another Type 89. This may have been the aircraft of the Kaga's Commander, Air Group (CAG) Commander Iwai who was killed in this action along with his deputy. Lieutenant Wang Wen-Hua caught two Type 89's trying to attack Schien-chiao from the south and shot one down in flames. One of the crew, a young ensign, bailed out and was captured. (This unnamed ensign later defected to the Chinese side and helped translate decoded Japanese radio messages). Lieutenant Yuan Chin-Han in No. 2108 went after the No.1 Shotai in a formation and claimed to have shot down the leader in flames (this may also have been Iwai's plane, it is almost certain that many Chinese pilots shot at the same planes). Lieutenant Liu Chi-Sheng in No. 2102 also claimed one Type 89 over Woong-Chia-Fu but was hit in the fuel tank and force landed at Chaio-shi Airfield where his plane was further damaged by bombing.
Lieutenant Le Yi-Chin from the 22nd PS made no less than 4 claims but these are almost certainly duplicates of other claims or overoptimistic.
Deputy Squadron C.O. Lai Ming-Tang landed to refuel and took off again to claim a shared kill with his wingman Lieutenant Liang Tian-Cheng.
Of the 23rd PS, Captain Mao Ying-Chu, Lieutenant Yang Yu-Ching and Lieutenant Wang Yin-Hua each claimed one Type 89.

Later in the day at 13:30 the Nanking Air Defence Command received a report that 16 Japanese aircraft had flown past Soochow towards Nanking. The alarm was sounded, and Chinese Air Force fighters took off to meet them. The Japanese aircraft were 20 G3Ms from the Kisarazu Ku. The Japanese aircraft had flown in directly from Ohmura in Japan and landed back at Cheju-do.
From Chu Yung, squadrons of the 3rd PG scrambled their aircraft. Wong Pan-Yang led eight Boeing 281s from the 17th PS. Chen Yau-Wei, Commander of the 8th PS, led five Fiat CR.32 fighters. Scrambled were also seven Hawk IIs from the 28th PS, 5th PG, and one Hawk III and five Hawk II from the 34th Provisional PS.
In the ensuing melee, four G3Ms were shot down and six damaged. Claims were confused but it is generally acknowledged that Captain Wong Sun-Shui (in #1703) downed the first G3M to fall in the Battle of Nanking when the eight Boeings from the 17th PS attacked a flight of six Mitsubishi G3M bombers over Nanking and claimed to have shot them all down without losses. This was the No.4 aircraft in a Shotai that bombed the Ta Hsiao-chang Airfield, most likely the No. 5 Shotai led by Lieutenant Yoshida. 17th PS’ Wong Pan-Yang and Su Ying-Hsien shared one victory at Chu-Yung while Chun Chia-Chu claimed another, which crashed south-east of Nanking. Chin Shui-Tin also took part in this interception but didn't claim any aircraft.
The Japanese aircraft fled and the 8th PS went after them. Chen Yau-Wei and Huang Chu-Ku shared a victory near Chu-Yung while Shen Tse-Liu and Liu Chi-Wei together shot down an enemy plane west of Lui Shui.
Captain Chow Ting-Fong, commander of the 34th PS led six Hawks from Chia Hsiang and followed eight Japanese aircraft to Nanking. Captain Chow attacked one of these and shot it down over Fang Shan.
4th PG’s Captain Lee Kuei-Tan led three Hawk IIIs of the 21st PS and Captain Huang Kuang-Han, C.O. of the 22nd PS, led eight Hawk IIIs from Hangchow to Nanking to help in this interception and they also attacked the bombers. Lee Kuei-Tan claimed a shared bomber together with three other pilots. Tan Won and Yuan Chin-Han shared a victory. Cheng Hsiao-Yu, Pa Ching-Cheng and Wu Ting-Chun each claimed one shot down. Wu Ting-Chun’s aircraft was damaged in this combat and he was forced to make an emergency landing. Liang Tian-Cheng claimed two victories. Huang Kuang-Han claimed a Japanese G3M halfway between Nanking and Lui Shui.
Because of low clouds, each group fought on it’s own with little co-ordination. A total of 14 Japanese aircraft were claimed shot down. Five Chinese aircraft were damaged.

During an attack on Japanese positions near Shanghai in the afternoon on 3 September flight leader Tan Won’s Hawk III (no. 2310) was damaged. He returned to Da Jiao-Chang airfield in his damaged fighter at 17:30.
It seems that the Hawk was a write-off.

Tan Won ended the war with 1 biplane victory, this one being claimed while flying the Curtiss Hawk III.

Claims:

Kill no.	Date	Time	Number	Type	Result	Plane type	Serial no.	Locality	Unit
	1937
	14/08/37	17:00-	1/2	G3M1 (a)	Shared destroyed	Curtiss Hawk III		Ban Shan	21st PS
1	15/08/37		1	Type 89 (b)	Destroyed	Curtiss Hawk III	#2104	Hangchow area	21st PS
	15/08/37		1/2	G3M (c)	Shared destroyed	Curtiss Hawk III		Nanking area	21st PS

Biplane victories: 1 and 2 shared destroyed.
TOTAL: 1 and 2 shared destroyed.
(a) Mitsubishi G3M1 Model 11 from 1st Shotai of Kanoya Kokutai, IJNAF, which crashed burning near the town of Ban Shan.
(b) Claimed in combat with Type 89 torpedo bombers from the Japanese carrier Kaga. The Chinese pilots claimed 17 destroyed enemy aircraft but the actual losses were six shot down and two ditched in Hangchow Bay.
(c) Probably claimed in combat with the Kisarazu Ku.

Sources:
China Incident (Air Enthusiast/April 1973) - Victor Chun, 1973 kindly provided by Börje Henningsson
Tidbits from the Sino-Japanese Air Battles - Chang Kuang-Ming, 1998 World News Weekly August 1998 kindly provided by Tom Chan
Information kindly provided by Raymond Cheung, Tom Chan, Jack Hwang and Erich Wang.