68311
A tandem , two-seat aircraft designed around the dynamic drive and rotor systems of the Sikorsky S-61 , it was designed to serve as an attack helicopter or to transport up to eight troops into combat .
 Sikorsky S-61
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 Sikorsky S-61