Question: what sonar device let morse code messages be sent underwater from a submarine in 1915
[{'answer': 'Fessenden', 'provenance': [{'wikipedia_id': '27639129', 'title': 'Fessenden oscillator', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 9, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]