[Hugh]

Here are some 1944-45 sets of North China Japanese Occupation stamps. 

They were issued for use in Hunan, Hebei, Shanxi, Shandong and Norther Jiangsu.

   

Stamps:
North China Japanese Occupation Stamps
Overprints on earlier stamps of Sun Yat-sen and Martyr / Chen Ying-shih
[Note: Lower overprints are printed R to L on stamps]

Series: 6th Anniversary of the General Post Office of North China
Issued on August 15, 1944
Upper Overprint, black: 北 華 [North China]
Lower Overprint, red / blue: 郵政總局成立 / 六周年紀念 [The establishment of the General Post Office / Commemoration of the sixth anniversary]
Sc. 8N95 - 98

The Japanese set up a regional GPO at Beijing in June 1938.

Series: Commemoration of the Death of Wang Ching-wei (Wang Jingwei (1883-1944)
[President of the Reorganized National Government of the Republic of China (1940-1944), a puppet state of the Empire of Japan]
Issued on December 5, 1944
Upper Overprint, black: 北 華 [North China]
Lower Overprint, black / blue: 汪主席 / 葬典紀念 [Chairman Wang / Funeral Commemoration]
Sc. 8N99 - 102

Following the outbreak of the Second Sino-Japanese War in 1937, Wang accepted an invitation from the Japanese to form a collaborationist government in Nanjing, of which he served as the head of state until his death shortly before the end of World War II in Asia.

Series: Commemoration of the 2nd Anniversary of the Declaration of War
Issued on January 9, 1945
Upper Overprint, black: 北 華 [North China]
Lower Overprint, red / black: 參戰二周年 / 紀念 [The second anniversary of the war / Commemoration]
Sc. 8N103 - 106

These four stamps refer to the 2nd anniversary of the January 9, 1943 declaration of war on the US and UK by the 'Reorganized Government' in Nanjin