Mezue ahịrịokwu na-esonụ: RDF mbụ nke Royal Navy nwere ihe ịga nke ọma bụ "Type 79Y Surface Warning", nke a nwalere n'oké osimiri na mmalite 1938. John D. S. Rawlinson bụ onye nduzi nke ọrụ ahụ. Nke a 43-MHz (7-m), 70-kW setịpụrụ na-eji ntanye nnyefe na ịnweta antenna ma nwee ebe dị anya site na 30 ruo 50 kilomita, dabere na elu antenna. Ka ọ na-erule 1940, nke a ghọrọ "Type 281", mụbara ugboro ugboro na 85 MHz (3.5 m) na ike dị n'etiti 350 na 1,000 kW, dabere na obosara pulse. Site na antenna ndị a na-eduzi, a na-ejikwa ya maka Njikwa Ngwá Agha. E ji nke a mee ihe na mbuso agha na
March 1941 nwere ihe ịga nke ọma dị ukwuu. "Type 281B" na-eji otu transmitting na anata poolu. "Type 281", gụnyere ụdị B, bụ usoro metrik nke Royal Navy nke a nwalere n'agha n'oge agha ahụ.