Terms such as trans-pacific, trans-atlantic, China clipper, Pacific clipper covers, Pan-American airways etc are very confusing to me; so I decided to read up on the topic and skim through the vast resources in the internet. These terms are quite important to know because many interesting and unique pre-WWII covers bear these words and not knowing them means you'll miss some of the greatest things in collecting postal history.

Brief History of the Trans-Pacific Clipper Service

Trans-Pacific and Trans-Atlantic are just two of the many routes in the Pan American Airways service. The Pan American Airways (PanAm) was the premier American air carrier from 1920s before its collapse in 1991. "Clipper" simply refers to a 19th century sailing ship but the term is very synonymous to the company because they named their aircrafts with the word "clipper" (e.g. China clipper). This is probably to show the image of sailing through the blue sky to exotic and distant destinations.



The China Clipper passes over the San Francisco waterfront at the start of the inaugural commercial flight across the Pacific Ocean.


China clipper is the name for one of the company's aircraft, and is esentially a Martin M-130 flying boat. Only three M-130s were built: China clipper, Hawaii clipper and the Phillipine clipper. A fourth flying boat called the Russian clipper (designated M-156) was built for the Soviet Union. The China clipper, being the first of the four flying boats of the company, is important because it was the first airmail flight across the Pacific. On November 22, 1935, China clipper 'sailed' from San Francisco for Manila. This event marked the first trans-pacific airmail flight.



A cover sent to US President, Franklin D. Roosevelt from the trans-Pacific first flight



The Trans-Pacific Route

The first trans-Pacific route was designated FAM-14 (Foreign Air Mail Route). From 1935-1939, FAM-14 served as the only route connecting USA to Asia. However, as the World War II seemed inevitable and fears of normal delivery being attacked, the volume of mails carried in the Pacific clipper service began to increase. This prompted the Pan American Airways to open another route in the Pacific region, designated FAM-19, connecting the US and southern Pacific with Auckland as a base.

When Italy joined the WWII conflict in 1940, all existing Mediterranean routes for airmails were esentially stopped. This means letters from Asia could not be delivered to western European countries through the Mediterranean routes. As a result, two-oceans airmail service was developed, the trans-Pacific, trans-Atlantic route. In general, the Pacific clipper service was much safer, faster and reliable, but also more expensive. This explains why covers flown in the service are usually franked with high values stamps.

North Borneo and the Clipper service

The Pacific clipper service only became available in Singapore in May 1941. Several covers from North Borneo were sent using the service. This is usually characterised by high-value frankings and absence of incoming postmark (eg. Singapore). The last flight of the China clipper left Singapore on November 30, 1941 and arrived Manila the same day. It departed Manila on December 1 and arrived San Francisco on Dec 6. For only a brief period of availability, covers from North Borneo, Sarawak, Malaya etc flown via the clipper are considered very rare.

The rates for the service with regards to North Borneo depends on the service used. From May 26, 1941 ½ oz. letter to Europe via Egypt costs 55c, Europe destination with air to NY and then by sea costs $1.45, while with air throughout (i.e. trans-Pacific, trans-Atlantic) costs $2.05. US and Canada destinations costs $1.45 however, on July 3, 1941 the rate was raised to $1.55 per ½oz. Postcards have lower rates. In addition to the standard clipper rates, 2 cent War Tax stamp (for non-domestic destination) is also usually charged.

Summary

China clipper = Name of first flying boat Martin M-130 across the Pacific from USA

Trans- Pacific = Can be FAM-14 or FAM-19, routes of airmails across the Pacific

Trans-Pacific trans-Atlantic = Two oceans service crossing the Pacific and Atlantic oceans by air throughout

References:

Gracephilatelics

Wikipedia

Etc

Further Reading: Sarawak mail carried by the Pan American Airways during WWII
North Borneo Stamps in The Stamps Journal