According to 『The Journal of Hamel』, they were sent to Namhansanseong everytime the envoys of the Ching Dynasty visited Seoul and going out was prohibited by order of the king.
It shows how nervous Joseon was because it was secretly keeping Hamel and his mates from the Ching Dynasty.


Apparently, their Western technology of weapon was valuable enough to be attached to Hullyeondogam to contribute to King Hyojong's policy of expedition to the north.

However, training 35 foreigners(originally they were 36, but one of them died in Yeongam on their way to Seoul) in Hullyeondogam may create a doubt of the Ching Dynasty, resulting in hindering the expedition to the north.

When Hamel and his mates stayed in Seoul, the envoys of the Ching Dynasty visited Seoul four times. Between August and September in 1654 when the envoys of the Ching Dynasty visited Seoul for the first time, Hamel and his mates stayed in Namhansanseong and their existence was out of question.

In March, 1655 when the envoys of the Ching Dynasty visited Seoul, a grave situation happened.

As before, Hamel and his mates were not allowed to go out and ordered and punish will be mete out for violation. But two of the Dutch escaped from their place of residence and jumped into the envoys' return procession asking them to sent back home.

These people were Hendrik Janse, a chief officer, born in Amsterdam and Hendrik Janse Bos, a gunner, born in Harrlem.

Fortunately, this incident was straightened after the envoys received bribes. The Joseon government did not want a repeat of such kind of incident to happen again. In a coincidence the two leaders of this incident died in prison later.

Although Hamel had a doubt whether they died naturally or executed. As related in Korean historical material(『Hyojongsillok』, the 6th year of King Hyojong) it was said that Hendrik Janse (Nam Buksan in Korean name) was very irritated in prison that he did not eat at all, and finally succumbed to a diseaseand died. However there was no mention about the death Hendrik Janse Bos (Nam Ian in Korean name).

Hamel and his other mates were examined if they knew about the plan. They were to be given 50 blows on their bare buttocks to let them know that escape was impossible.

However, this punishment was canceled by order of King Hyojong because they came to Joseon by shipwreck and not for plunder.

After that, Hamel and his mates were kept under much closer observation. After this incident, the envoys of the Ching Dynasty visited Seoul twice more, and each visit Hamel and his mates were severely confined.